idb wip

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diff --git a/packages/idb-bridge/src/tree/b+tree.ts b/packages/idb-bridge/src/tree/b+tree.ts
new file mode 100644
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+++ b/packages/idb-bridge/src/tree/b+tree.ts
@@ -0,0 +1,1351 @@
+/*
+Copyright (c) 2018 David Piepgrass
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+SPDX-License-Identifier: MIT
+*/
+
+// Original repository: https://github.com/qwertie/btree-typescript
+
+
+import { ISortedMap, ISortedMapF } from './interfaces';
+export {
+  ISetSource, ISetSink, ISet, ISetF, ISortedSetSource, ISortedSet, ISortedSetF,
+  IMapSource, IMapSink, IMap, IMapF, ISortedMapSource, ISortedMap, ISortedMapF
+} from './interfaces';
+
+export type EditRangeResult<V,R=number> = {value?:V, break?:R, delete?:boolean};
+
+type index = number;
+
+// Informative microbenchmarks & stuff:
+// http://www.jayconrod.com/posts/52/a-tour-of-v8-object-representation (very educational)
+// https://blog.mozilla.org/luke/2012/10/02/optimizing-javascript-variable-access/ (local vars are faster than properties)
+// http://benediktmeurer.de/2017/12/13/an-introduction-to-speculative-optimization-in-v8/ (other stuff)
+// https://jsperf.com/js-in-operator-vs-alternatives (avoid 'in' operator; `.p!==undefined` faster than `hasOwnProperty('p')` in all browsers)
+// https://jsperf.com/instanceof-vs-typeof-vs-constructor-vs-member (speed of type tests varies wildly across browsers)
+// https://jsperf.com/detecting-arrays-new (a.constructor===Array is best across browsers, assuming a is an object)
+// https://jsperf.com/shallow-cloning-methods (a constructor is faster than Object.create; hand-written clone faster than Object.assign)
+// https://jsperf.com/ways-to-fill-an-array (slice-and-replace is fastest)
+// https://jsperf.com/math-min-max-vs-ternary-vs-if (Math.min/max is slow on Edge)
+// https://jsperf.com/array-vs-property-access-speed (v.x/v.y is faster than a[0]/a[1] in major browsers IF hidden class is constant)
+// https://jsperf.com/detect-not-null-or-undefined (`x==null` slightly slower than `x===null||x===undefined` on all browsers)
+// Overall, microbenchmarks suggest Firefox is the fastest browser for JavaScript and Edge is the slowest.
+// Lessons from https://v8project.blogspot.com/2017/09/elements-kinds-in-v8.html:
+//   - Avoid holes in arrays. Avoid `new Array(N)`, it will be "holey" permanently.
+//   - Don't read outside bounds of an array (it scans prototype chain).
+//   - Small integer arrays are stored differently from doubles
+//   - Adding non-numbers to an array deoptimizes it permanently into a general array
+//   - Objects can be used like arrays (e.g. have length property) but are slower
+//   - V8 source (NewElementsCapacity in src/objects.h): arrays grow by 50% + 16 elements
+
+/** Compares two numbers, strings, arrays of numbers/strings, Dates,
+ *  or objects that have a valueOf() method returning a number or string. 
+ *  Optimized for numbers. Returns 1 if a>b, -1 if a<b, and 0 if a===b.
+ */
+export function defaultComparator(a: any, b: any) {
+  var c = a - b;
+  if (c === c) return c; // a & b are number
+  // General case (c is NaN): string / arrays / Date / incomparable things
+  if (a) a = a.valueOf();
+  if (b) b = b.valueOf();
+  return a < b ? -1 : a > b ? 1 : a == b ? 0 : c;   
+};
+
+/**
+ * A reasonably fast collection of key-value pairs with a powerful API. 
+ * Largely compatible with the standard Map. BTree is a B+ tree data structure,
+ * so the collection is sorted by key.
+ * 
+ * B+ trees tend to use memory more efficiently than hashtables such as the
+ * standard Map, especially when the collection contains a large number of 
+ * items. However, maintaining the sort order makes them modestly slower: 
+ * O(log size) rather than O(1). This B+ tree implementation supports O(1)
+ * fast cloning. It also supports freeze(), which can be used to ensure that
+ * a BTree is not changed accidentally.
+ * 
+ * Confusingly, the ES6 Map.forEach(c) method calls c(value,key) instead of
+ * c(key,value), in contrast to other methods such as set() and entries()
+ * which put the key first. I can only assume that the order was reversed on 
+ * the theory that users would usually want to examine values and ignore keys.
+ * BTree's forEach() therefore works the same way, but a second method 
+ * `.forEachPair((key,value)=>{...})` is provided which sends you the key
+ * first and the value second; this method is slightly faster because it is 
+ * the "native" for-each method for this class.
+ * 
+ * Out of the box, BTree supports keys that are numbers, strings, arrays of 
+ * numbers/strings, Date, and objects that have a valueOf() method returning a 
+ * number or string. Other data types, such as arrays of Date or custom
+ * objects, require a custom comparator, which you must pass as the second 
+ * argument to the constructor (the first argument is an optional list of 
+ * initial items). Symbols cannot be used as keys because they are unordered
+ * (one Symbol is never "greater" or "less" than another).
+ * 
+ * @example
+ * Given a {name: string, age: number} object, you can create a tree sorted by
+ * name and then by age like this:
+ *   
+ *     var tree = new BTree(undefined, (a, b) => {
+ *       if (a.name > b.name)
+ *         return 1; // Return a number >0 when a > b
+ *       else if (a.name < b.name)
+ *         return -1; // Return a number <0 when a < b
+ *       else // names are equal (or incomparable)
+ *         return a.age - b.age; // Return >0 when a.age > b.age
+ *     });
+ * 
+ *     tree.set({name:"Bill", age:17}, "happy");
+ *     tree.set({name:"Fran", age:40}, "busy & stressed");
+ *     tree.set({name:"Bill", age:55}, "recently laid off");
+ *     tree.forEachPair((k, v) => {
+ *       console.log(`Name: ${k.name} Age: ${k.age} Status: ${v}`);
+ *     });
+ * 
+ * @description
+ * The "range" methods (`forEach, forRange, editRange`) will return the number
+ * of elements that were scanned. In addition, the callback can return {break:R}
+ * to stop early and return R from the outer function.
+ * 
+ * - TODO: Test performance of preallocating values array at max size
+ * - TODO: Add fast initialization when a sorted array is provided to constructor
+ * 
+ * For more documentation see https://github.com/qwertie/btree-typescript
+ *
+ * Are you a C# developer? You might like the similar data structures I made for C#: 
+ * BDictionary, BList, etc. See http://core.loyc.net/collections/
+ * 
+ * @author David Piepgrass
+ */
+export default class BTree<K=any, V=any> implements ISortedMapF<K,V>, ISortedMap<K,V>
+{
+  private _root: BNode<K, V> = EmptyLeaf as BNode<K,V>;
+  _size: number = 0;
+  _maxNodeSize: number;
+  _compare: (a:K, b:K) => number;
+  
+  /**
+   * Initializes an empty B+ tree.
+   * @param compare Custom function to compare pairs of elements in the tree.
+   *   This is not required for numbers, strings and arrays of numbers/strings.
+   * @param entries A set of key-value pairs to initialize the tree
+   * @param maxNodeSize Branching factor (maximum items or children per node)
+   *   Must be in range 4..256. If undefined or <4 then default is used; if >256 then 256.
+   */
+  public constructor(entries?: [K,V][], compare?: (a: K, b: K) => number, maxNodeSize?: number) {
+    this._maxNodeSize = maxNodeSize! >= 4 ? Math.min(maxNodeSize!, 256) : 32;
+    this._compare = compare || defaultComparator;
+    if (entries)
+      this.setPairs(entries);
+  }
+  
+  // ES6 Map<K,V> methods ///////////////////////////////////////////////////
+
+  /** Gets the number of key-value pairs in the tree. */
+  get size() { return this._size; }
+  /** Gets the number of key-value pairs in the tree. */
+  get length() { return this._size; }
+  /** Returns true iff the tree contains no key-value pairs. */
+  get isEmpty() { return this._size === 0; }
+
+  /** Releases the tree so that its size is 0. */
+  clear() {
+    this._root = EmptyLeaf as BNode<K,V>;
+    this._size = 0;
+  }
+
+  forEach(callback: (v:V, k:K, tree:BTree<K,V>) => void, thisArg?: any): number;
+
+  /** Runs a function for each key-value pair, in order from smallest to 
+   *  largest key. For compatibility with ES6 Map, the argument order to
+   *  the callback is backwards: value first, then key. Call forEachPair 
+   *  instead to receive the key as the first argument.
+   * @param thisArg If provided, this parameter is assigned as the `this`
+   *        value for each callback.
+   * @returns the number of values that were sent to the callback,
+   *        or the R value if the callback returned {break:R}. */
+  forEach<R=number>(callback: (v:V, k:K, tree:BTree<K,V>) => {break?:R}|void, thisArg?: any): R|number {
+    if (thisArg !== undefined)
+      callback = callback.bind(thisArg);
+    return this.forEachPair((k, v) => callback(v, k, this));
+  }
+
+  /** Runs a function for each key-value pair, in order from smallest to 
+   *  largest key. The callback can return {break:R} (where R is any value
+   *  except undefined) to stop immediately and return R from forEachPair.
+   * @param onFound A function that is called for each key-value pair. This 
+   *        function can return {break:R} to stop early with result R.
+   *        The reason that you must return {break:R} instead of simply R 
+   *        itself is for consistency with editRange(), which allows 
+   *        multiple actions, not just breaking.
+   * @param initialCounter This is the value of the third argument of 
+   *        `onFound` the first time it is called. The counter increases 
+   *        by one each time `onFound` is called. Default value: 0
+   * @returns the number of pairs sent to the callback (plus initialCounter,
+   *        if you provided one). If the callback returned {break:R} then
+   *        the R value is returned instead. */
+  forEachPair<R=number>(callback: (k:K, v:V, counter:number) => {break?:R}|void, initialCounter?: number): R|number {
+    var low = this.minKey(), high = this.maxKey();
+    return this.forRange(low!, high!, true, callback, initialCounter);
+  }
+
+  /**
+   * Finds a pair in the tree and returns the associated value.
+   * @param defaultValue a value to return if the key was not found.
+   * @returns the value, or defaultValue if the key was not found.
+   * @description Computational complexity: O(log size)
+   */
+  get(key: K, defaultValue?: V): V | undefined {
+    return this._root.get(key, defaultValue, this);
+  }
+  
+  /**
+   * Adds or overwrites a key-value pair in the B+ tree.
+   * @param key the key is used to determine the sort order of
+   *        data in the tree.
+   * @param value data to associate with the key (optional)
+   * @param overwrite Whether to overwrite an existing key-value pair 
+   *        (default: true). If this is false and there is an existing
+   *        key-value pair then this method has no effect.
+   * @returns true if a new key-value pair was added.
+   * @description Computational complexity: O(log size)
+   * Note: when overwriting a previous entry, the key is updated
+   * as well as the value. This has no effect unless the new key
+   * has data that does not affect its sort order.
+   */
+  set(key: K, value: V, overwrite?: boolean): boolean { 
+    if (this._root.isShared)
+      this._root = this._root.clone();
+    var result = this._root.set(key, value, overwrite, this);
+    if (result === true || result === false)
+      return result;
+    // Root node has split, so create a new root node.
+    this._root = new BNodeInternal<K,V>([this._root, result]);
+    return true;
+  }
+
+  /**
+   * Returns true if the key exists in the B+ tree, false if not.
+   * Use get() for best performance; use has() if you need to
+   * distinguish between "undefined value" and "key not present".
+   * @param key Key to detect
+   * @description Computational complexity: O(log size)
+   */
+  has(key: K): boolean { 
+    return this.forRange(key, key, true, undefined) !== 0;
+  }
+
+  /**
+   * Removes a single key-value pair from the B+ tree.
+   * @param key Key to find
+   * @returns true if a pair was found and removed, false otherwise.
+   * @description Computational complexity: O(log size)
+   */
+  delete(key: K): boolean {
+    return this.editRange(key, key, true, DeleteRange) !== 0;
+  }
+
+  // Clone-mutators /////////////////////////////////////////////////////////
+
+  /** Returns a copy of the tree with the specified key set (the value is undefined). */
+  with(key: K): BTree<K,V|undefined>;
+  /** Returns a copy of the tree with the specified key-value pair set. */
+  with<V2>(key: K, value: V2, overwrite?: boolean): BTree<K,V|V2>;
+  with<V2>(key: K, value?: V2, overwrite?: boolean): BTree<K,V|V2|undefined> {
+    let nu = this.clone() as BTree<K,V|V2|undefined>;
+    return nu.set(key, value, overwrite) || overwrite ? nu : this;
+  }
+
+  /** Returns a copy of the tree with the specified key-value pairs set. */
+  withPairs<V2>(pairs: [K,V|V2][], overwrite: boolean): BTree<K,V|V2> {
+    let nu = this.clone() as BTree<K,V|V2>;
+    return nu.setPairs(pairs, overwrite) !== 0 || overwrite ? nu : this;
+  }
+
+  /** Returns a copy of the tree with the specified keys present. 
+   *  @param keys The keys to add. If a key is already present in the tree,
+   *         neither the existing key nor the existing value is modified.
+   *  @param returnThisIfUnchanged if true, returns this if all keys already 
+   *  existed. Performance note: due to the architecture of this class, all
+   *  node(s) leading to existing keys are cloned even if the collection is
+   *  ultimately unchanged.
+  */
+  withKeys(keys: K[], returnThisIfUnchanged?: boolean): BTree<K,V|undefined> {
+    let nu = this.clone() as BTree<K,V|undefined>, changed = false;
+    for (var i = 0; i < keys.length; i++)
+      changed = nu.set(keys[i], undefined, false) || changed;
+    return returnThisIfUnchanged && !changed ? this : nu;
+  }
+
+  /** Returns a copy of the tree with the specified key removed. 
+   * @param returnThisIfUnchanged if true, returns this if the key didn't exist.
+   *  Performance note: due to the architecture of this class, node(s) leading
+   *  to where the key would have been stored are cloned even when the key
+   *  turns out not to exist and the collection is unchanged.
+   */
+  without(key: K, returnThisIfUnchanged?: boolean): BTree<K,V> {
+    return this.withoutRange(key, key, true, returnThisIfUnchanged);
+  }
+
+  /** Returns a copy of the tree with the specified keys removed.
+   * @param returnThisIfUnchanged if true, returns this if none of the keys
+   *  existed. Performance note: due to the architecture of this class,
+   *  node(s) leading to where the key would have been stored are cloned
+   *  even when the key turns out not to exist.
+   */
+  withoutKeys(keys: K[], returnThisIfUnchanged?: boolean): BTree<K,V> {
+    let nu = this.clone();
+    return nu.deleteKeys(keys) || !returnThisIfUnchanged ? nu : this;
+  }
+
+  /** Returns a copy of the tree with the specified range of keys removed. */
+  withoutRange(low: K, high: K, includeHigh: boolean, returnThisIfUnchanged?: boolean): BTree<K,V> {
+    let nu = this.clone();
+    if (nu.deleteRange(low, high, includeHigh) === 0 && returnThisIfUnchanged)
+      return this;
+    return nu;
+  }
+
+  /** Returns a copy of the tree with pairs removed whenever the callback 
+   *  function returns false. `where()` is a synonym for this method. */
+  filter(callback: (k:K,v:V,counter:number) => boolean, returnThisIfUnchanged?: boolean): BTree<K,V> {
+    var nu = this.greedyClone();
+    var del: any;
+    nu.editAll((k,v,i) => {
+      if (!callback(k, v, i)) return del = Delete;
+    });
+    if (!del && returnThisIfUnchanged)
+      return this;
+    return nu;
+  }
+
+  /** Returns a copy of the tree with all values altered by a callback function. */
+  mapValues<R>(callback: (v:V,k:K,counter:number) => R): BTree<K,R> {
+    var tmp = {} as {value:R};
+    var nu = this.greedyClone();
+    nu.editAll((k,v,i) => {
+      return tmp.value = callback(v, k, i), tmp as any;
+    });
+    return nu as any as BTree<K,R>;
+  }
+
+  /** Performs a reduce operation like the `reduce` method of `Array`. 
+   *  It is used to combine all pairs into a single value, or perform 
+   *  conversions. `reduce` is best understood by example. For example,
+   *  `tree.reduce((P, pair) => P * pair[0], 1)` multiplies all keys 
+   *  together. It means "start with P=1, and for each pair multiply 
+   *  it by the key in pair[0]". Another example would be converting 
+   *  the tree to a Map (in this example, note that M.set returns M):
+   *  
+   *  var M = tree.reduce((M, pair) => M.set(pair[0],pair[1]), new Map())
+   *  
+   *  **Note**: the same array is sent to the callback on every iteration.
+   */
+  reduce<R>(callback: (previous:R,currentPair:[K,V],counter:number,tree:BTree<K,V>) => R, initialValue: R): R;
+  reduce<R>(callback: (previous:R|undefined,currentPair:[K,V],counter:number,tree:BTree<K,V>) => R): R|undefined;
+  reduce<R>(callback: (previous:R|undefined,currentPair:[K,V],counter:number,tree:BTree<K,V>) => R, initialValue?: R): R|undefined {
+    let i = 0, p = initialValue;
+    var it = this.entries(this.minKey(), ReusedArray), next;
+    while (!(next = it.next()).done)
+      p = callback(p, next.value, i++, this);
+    return p;
+  }
+
+  // Iterator methods ///////////////////////////////////////////////////////
+
+  /** Returns an iterator that provides items in order (ascending order if
+   *  the collection's comparator uses ascending order, as is the default.)
+   *  @param lowestKey First key to be iterated, or undefined to start at
+   *         minKey(). If the specified key doesn't exist then iteration
+   *         starts at the next higher key (according to the comparator).
+   *  @param reusedArray Optional array used repeatedly to store key-value
+   *         pairs, to avoid creating a new array on every iteration.
+   */
+  entries(lowestKey?: K, reusedArray?: (K|V)[]): IterableIterator<[K,V]> {
+    var info = this.findPath(lowestKey);
+    if (info === undefined) return iterator<[K,V]>();
+    var {nodequeue, nodeindex, leaf} = info;
+    var state = reusedArray !== undefined ? 1 : 0;
+    var i = (lowestKey === undefined ? -1 : leaf.indexOf(lowestKey, 0, this._compare) - 1);
+
+    return iterator<[K,V]>(() => {
+      jump: for (;;) {
+        switch(state) {
+          case 0:
+            if (++i < leaf.keys.length)
+              return {done: false, value: [leaf.keys[i], leaf.values[i]]};
+            state = 2;
+            continue;
+          case 1:
+            if (++i < leaf.keys.length) {
+              reusedArray![0] = leaf.keys[i], reusedArray![1] = leaf.values[i];
+              return {done: false, value: reusedArray as [K,V]};
+            }
+            state = 2;
+          case 2:
+            // Advance to the next leaf node
+            for (var level = -1;;) {
+              if (++level >= nodequeue.length) {
+                state = 3; continue jump;
+              }
+              if (++nodeindex[level] < nodequeue[level].length)
+                break;
+            }
+            for (; level > 0; level--) {
+              nodequeue[level-1] = (nodequeue[level][nodeindex[level]] as BNodeInternal<K,V>).children;
+              nodeindex[level-1] = 0;
+            }
+            leaf = nodequeue[0][nodeindex[0]];
+            i = -1;
+            state = reusedArray !== undefined ? 1 : 0;
+            continue;
+          case 3:
+            return {done: true, value: undefined};
+        }
+      }
+    });
+  }
+
+  /** Returns an iterator that provides items in reversed order.
+   *  @param highestKey Key at which to start iterating, or undefined to 
+   *         start at minKey(). If the specified key doesn't exist then iteration
+   *         starts at the next lower key (according to the comparator).
+   *  @param reusedArray Optional array used repeatedly to store key-value
+   *         pairs, to avoid creating a new array on every iteration.
+   *  @param skipHighest Iff this flag is true and the highestKey exists in the
+   *         collection, the pair matching highestKey is skipped, not iterated.
+   */
+  entriesReversed(highestKey?: K, reusedArray?: (K|V)[], skipHighest?: boolean): IterableIterator<[K,V]> {
+    if ((highestKey = highestKey || this.maxKey()) === undefined)
+      return iterator<[K,V]>(); // collection is empty
+    var {nodequeue,nodeindex,leaf} = this.findPath(highestKey) || this.findPath(this.maxKey())!;
+    check(!nodequeue[0] || leaf === nodequeue[0][nodeindex[0]], "wat!");
+    var i = leaf.indexOf(highestKey, 0, this._compare);
+    if (!(skipHighest || this._compare(leaf.keys[i], highestKey) > 0))
+      i++;
+    var state = reusedArray !== undefined ? 1 : 0;
+
+    return iterator<[K,V]>(() => {
+      jump: for (;;) {
+        switch(state) {
+          case 0:
+            if (--i >= 0)
+              return {done: false, value: [leaf.keys[i], leaf.values[i]]};
+            state = 2;
+            continue;
+          case 1:
+            if (--i >= 0) {
+              reusedArray![0] = leaf.keys[i], reusedArray![1] = leaf.values[i];
+              return {done: false, value: reusedArray as [K,V]};
+            }
+            state = 2;
+          case 2:
+            // Advance to the next leaf node
+            for (var level = -1;;) {
+              if (++level >= nodequeue.length) {
+                state = 3; continue jump;
+              }
+              if (--nodeindex[level] >= 0)
+                break;
+            }
+            for (; level > 0; level--) {
+              nodequeue[level-1] = (nodequeue[level][nodeindex[level]] as BNodeInternal<K,V>).children;
+              nodeindex[level-1] = nodequeue[level-1].length-1;
+            }
+            leaf = nodequeue[0][nodeindex[0]];
+            i = leaf.keys.length;
+            state = reusedArray !== undefined ? 1 : 0;
+            continue;
+          case 3:
+            return {done: true, value: undefined};
+        }
+      }
+    });
+  }
+
+  /* Used by entries() and entriesReversed() to prepare to start iterating.
+   * It develops a "node queue" for each non-leaf level of the tree.
+   * Levels are numbered "bottom-up" so that level 0 is a list of leaf 
+   * nodes from a low-level non-leaf node. The queue at a given level L
+   * consists of nodequeue[L] which is the children of a BNodeInternal, 
+   * and nodeindex[L], the current index within that child list, such
+   * such that nodequeue[L-1] === nodequeue[L][nodeindex[L]].children.
+   * (However inside this function the order is reversed.)
+   */
+  private findPath(key?: K): { nodequeue: BNode<K,V>[][], nodeindex: number[], leaf: BNode<K,V> } | undefined
+  {
+    var nextnode = this._root;
+    var nodequeue: BNode<K,V>[][], nodeindex: number[];
+
+    if (nextnode.isLeaf) {
+      nodequeue = EmptyArray, nodeindex = EmptyArray; // avoid allocations
+    } else {
+      nodequeue = [], nodeindex = [];
+      for (var d = 0; !nextnode.isLeaf; d++) {
+        nodequeue[d] = (nextnode as BNodeInternal<K,V>).children;
+        nodeindex[d] = key === undefined ? 0 : nextnode.indexOf(key, 0, this._compare);
+        if (nodeindex[d] >= nodequeue[d].length)
+          return; // first key > maxKey()
+        nextnode = nodequeue[d][nodeindex[d]];
+      }
+      nodequeue.reverse();
+      nodeindex.reverse();
+    }
+    return {nodequeue, nodeindex, leaf:nextnode};
+  }
+
+  /** Returns a new iterator for iterating the keys of each pair in ascending order. 
+   *  @param firstKey: Minimum key to include in the output. */
+  keys(firstKey?: K): IterableIterator<K> {
+    var it = this.entries(firstKey, ReusedArray);
+    return iterator<K>(() => {
+      var n: IteratorResult<any> = it.next();
+      if (n.value) n.value = n.value[0];
+      return n;
+    });
+  }
+  
+  /** Returns a new iterator for iterating the values of each pair in order by key. 
+   *  @param firstKey: Minimum key whose associated value is included in the output. */
+  values(firstKey?: K): IterableIterator<V> {
+    var it = this.entries(firstKey, ReusedArray);
+    return iterator<V>(() => {
+      var n: IteratorResult<any> = it.next();
+      if (n.value) n.value = n.value[1];
+      return n;
+    });
+  }
+
+  // Additional methods /////////////////////////////////////////////////////
+
+  /** Returns the maximum number of children/values before nodes will split. */
+  get maxNodeSize() {
+    return this._maxNodeSize;
+  }
+
+  /** Gets the lowest key in the tree. Complexity: O(log size) */
+  minKey(): K | undefined { return this._root.minKey(); }
+  
+  /** Gets the highest key in the tree. Complexity: O(1) */
+  maxKey(): K | undefined { return this._root.maxKey(); }
+
+  /** Quickly clones the tree by marking the root node as shared. 
+   *  Both copies remain editable. When you modify either copy, any
+   *  nodes that are shared (or potentially shared) between the two
+   *  copies are cloned so that the changes do not affect other copies.
+   *  This is known as copy-on-write behavior, or "lazy copying". */
+  clone(): BTree<K,V> {
+    this._root.isShared = true;
+    var result = new BTree<K,V>(undefined, this._compare, this._maxNodeSize);
+    result._root = this._root;
+    result._size = this._size;
+    return result;
+  }
+
+  /** Performs a greedy clone, immediately duplicating any nodes that are 
+   *  not currently marked as shared, in order to avoid marking any nodes
+   *  as shared.
+   *  @param force Clone all nodes, even shared ones.
+   */
+  greedyClone(force?: boolean): BTree<K,V> {
+    var result = new BTree<K,V>(undefined, this._compare, this._maxNodeSize);
+    result._root = this._root.greedyClone(force);
+    result._size = this._size;
+    return result;
+  }
+
+  /** Gets an array filled with the contents of the tree, sorted by key */
+  toArray(maxLength: number = 0x7FFFFFFF): [K,V][] {
+    let min = this.minKey(), max = this.maxKey();
+    if (min !== undefined)
+      return this.getRange(min, max!, true, maxLength)
+    return [];
+  }
+
+  /** Gets an array of all keys, sorted */
+  keysArray() {
+    var results: K[] = [];
+    this._root.forRange(this.minKey()!, this.maxKey()!, true, false, this, 0, 
+      (k,v) => { results.push(k); });
+    return results;
+  }
+  
+  /** Gets an array of all values, sorted by key */
+  valuesArray() {
+    var results: V[] = [];
+    this._root.forRange(this.minKey()!, this.maxKey()!, true, false, this, 0,
+      (k,v) => { results.push(v); });
+    return results;
+  }
+
+  /** Gets a string representing the tree's data based on toArray(). */
+  toString() {
+    return this.toArray().toString();
+  }
+
+  /** Stores a key-value pair only if the key doesn't already exist in the tree. 
+   * @returns true if a new key was added
+  */
+  setIfNotPresent(key: K, value: V): boolean {
+    return this.set(key, value, false);
+  }
+
+  /** Returns the next pair whose key is larger than the specified key (or undefined if there is none) */
+  nextHigherPair(key: K): [K,V]|undefined {
+    var it = this.entries(key, ReusedArray);
+    var r = it.next();
+    if (!r.done && this._compare(r.value[0], key) <= 0)
+      r = it.next();
+    return r.value;
+  }
+  
+  /** Returns the next key larger than the specified key (or undefined if there is none) */
+  nextHigherKey(key: K): K|undefined {
+    var p = this.nextHigherPair(key);
+    return p ? p[0] : p;
+  }
+
+  /** Returns the next pair whose key is smaller than the specified key (or undefined if there is none) */
+  nextLowerPair(key: K): [K,V]|undefined {
+    var it = this.entriesReversed(key, ReusedArray, true);
+    return it.next().value;
+  }
+  
+  /** Returns the next key smaller than the specified key (or undefined if there is none) */
+  nextLowerKey(key: K): K|undefined {
+    var p = this.nextLowerPair(key);
+    return p ? p[0] : p;
+  }
+
+  /** Edits the value associated with a key in the tree, if it already exists. 
+   * @returns true if the key existed, false if not.
+  */
+  changeIfPresent(key: K, value: V): boolean { 
+    return this.editRange(key, key, true, (k,v) => ({value})) !== 0;
+  }
+
+  /**
+   * Builds an array of pairs from the specified range of keys, sorted by key.
+   * Each returned pair is also an array: pair[0] is the key, pair[1] is the value.
+   * @param low The first key in the array will be greater than or equal to `low`.
+   * @param high This method returns when a key larger than this is reached.
+   * @param includeHigh If the `high` key is present, its pair will be included
+   *        in the output if and only if this parameter is true. Note: if the
+   *        `low` key is present, it is always included in the output.
+   * @param maxLength Length limit. getRange will stop scanning the tree when 
+   *                  the array reaches this size.
+   * @description Computational complexity: O(result.length + log size)
+   */
+  getRange(low: K, high: K, includeHigh?: boolean, maxLength: number = 0x3FFFFFF): [K,V][] {
+    var results: [K,V][] = [];
+    this._root.forRange(low, high, includeHigh, false, this, 0, (k,v) => {
+      results.push([k,v])
+      return results.length > maxLength ? Break : undefined;
+    });
+    return results;
+  }
+
+  /** Adds all pairs from a list of key-value pairs.
+   * @param pairs Pairs to add to this tree. If there are duplicate keys, 
+   *        later pairs currently overwrite earlier ones (e.g. [[0,1],[0,7]] 
+   *        associates 0 with 7.)
+   * @param overwrite Whether to overwrite pairs that already exist (if false,
+   *        pairs[i] is ignored when the key pairs[i][0] already exists.)
+   * @returns The number of pairs added to the collection.
+   * @description Computational complexity: O(pairs.length * log(size + pairs.length))
+   */
+  setPairs(pairs: [K,V][], overwrite?: boolean): number {
+    var added = 0;
+    for (var i = 0; i < pairs.length; i++)
+      if (this.set(pairs[i][0], pairs[i][1], overwrite))
+        added++;
+    return added;
+  }
+
+  forRange(low: K, high: K, includeHigh: boolean, onFound?: (k:K,v:V,counter:number) => void, initialCounter?: number): number;
+
+  /**
+   * Scans the specified range of keys, in ascending order by key.
+   * Note: the callback `onFound` must not insert or remove items in the
+   * collection. Doing so may cause incorrect data to be sent to the 
+   * callback afterward.
+   * @param low The first key scanned will be greater than or equal to `low`.
+   * @param high Scanning stops when a key larger than this is reached.
+   * @param includeHigh If the `high` key is present, `onFound` is called for
+   *        that final pair if and only if this parameter is true.
+   * @param onFound A function that is called for each key-value pair. This 
+   *        function can return {break:R} to stop early with result R.
+   * @param initialCounter Initial third argument of onFound. This value 
+   *        increases by one each time `onFound` is called. Default: 0
+   * @returns The number of values found, or R if the callback returned 
+   *        `{break:R}` to stop early.
+   * @description Computational complexity: O(number of items scanned + log size)
+   */
+  forRange<R=number>(low: K, high: K, includeHigh: boolean, onFound?: (k:K,v:V,counter:number) => {break?:R}|void, initialCounter?: number): R|number {
+    var r = this._root.forRange(low, high, includeHigh, false, this, initialCounter || 0, onFound);
+    return typeof r === "number" ? r : r.break!;
+  }
+
+  /**
+   * Scans and potentially modifies values for a subsequence of keys.
+   * Note: the callback `onFound` should ideally be a pure function. 
+   *   Specfically, it must not insert items, call clone(), or change 
+   *   the collection except via return value; out-of-band editing may
+   *   cause an exception or may cause incorrect data to be sent to
+   *   the callback (duplicate or missed items). It must not cause a 
+   *   clone() of the collection, otherwise the clone could be modified
+   *   by changes requested by the callback.
+   * @param low The first key scanned will be greater than or equal to `low`.
+   * @param high Scanning stops when a key larger than this is reached.
+   * @param includeHigh If the `high` key is present, `onFound` is called for
+   *        that final pair if and only if this parameter is true.
+   * @param onFound A function that is called for each key-value pair. This 
+   *        function can return `{value:v}` to change the value associated 
+   *        with the current key, `{delete:true}` to delete the current pair,
+   *        `{break:R}` to stop early with result R, or it can return nothing
+   *        (undefined or {}) to cause no effect and continue iterating.
+   *        `{break:R}` can be combined with one of the other two commands.
+   *        The third argument `counter` is the number of items iterated 
+   *        previously; it equals 0 when `onFound` is called the first time.
+   * @returns The number of values scanned, or R if the callback returned 
+   *        `{break:R}` to stop early.
+   * @description 
+   *   Computational complexity: O(number of items scanned + log size)
+   *   Note: if the tree has been cloned with clone(), any shared
+   *   nodes are copied before `onFound` is called. This takes O(n) time 
+   *   where n is proportional to the amount of shared data scanned.
+   */
+  editRange<R=V>(low: K, high: K, includeHigh: boolean, onFound: (k:K,v:V,counter:number) => EditRangeResult<V,R>|void, initialCounter?: number): R|number {
+    var root = this._root;
+    if (root.isShared)
+      this._root = root = root.clone();
+    try {
+      var r = root.forRange(low, high, includeHigh, true, this, initialCounter || 0, onFound);
+      return typeof r === "number" ? r : r.break!;
+    } finally {
+      while (root.keys.length <= 1 && !root.isLeaf)
+        this._root = root = root.keys.length === 0 ? EmptyLeaf :
+                    (root as any as BNodeInternal<K,V>).children[0];
+    }
+  }
+
+  /** Same as `editRange` except that the callback is called for all pairs. */
+  editAll<R=V>(onFound: (k:K,v:V,counter:number) => EditRangeResult<V,R>|void, initialCounter?: number): R|number {
+    return this.editRange(this.minKey()!, this.maxKey()!, true, onFound, initialCounter);
+  }
+
+  /**
+   * Removes a range of key-value pairs from the B+ tree.
+   * @param low The first key scanned will be greater than or equal to `low`.
+   * @param high Scanning stops when a key larger than this is reached.
+   * @param includeHigh Specifies whether the `high` key, if present, is deleted.
+   * @returns The number of key-value pairs that were deleted.
+   * @description Computational complexity: O(log size + number of items deleted)
+   */
+  deleteRange(low: K, high: K, includeHigh: boolean): number {
+    return this.editRange(low, high, includeHigh, DeleteRange);
+  }
+
+  /** Deletes a series of keys from the collection. */
+  deleteKeys(keys: K[]): number {
+    for (var i = 0, r = 0; i < keys.length; i++)
+      if (this.delete(keys[i]))
+        r++;
+    return r;
+  }
+
+  /** Gets the height of the tree: the number of internal nodes between the 
+   *  BTree object and its leaf nodes (zero if there are no internal nodes). */
+  get height(): number {
+    for (var node = this._root, h = -1; node != null; h++)
+      node = (node as any).children;
+    return h;
+  }
+
+  /** Makes the object read-only to ensure it is not accidentally modified.
+   *  Freezing does not have to be permanent; unfreeze() reverses the effect.
+   *  This is accomplished by replacing mutator functions with a function 
+   *  that throws an Error. Compared to using a property (e.g. this.isFrozen) 
+   *  this implementation gives better performance in non-frozen BTrees.
+   */
+  freeze() {
+    var t = this as any;
+    // Note: all other mutators ultimately call set() or editRange() 
+    //       so we don't need to override those others.
+    t.clear = t.set = t.editRange = function() {
+      throw new Error("Attempted to modify a frozen BTree");
+    };
+  }
+
+  /** Ensures mutations are allowed, reversing the effect of freeze(). */
+  unfreeze() {
+    delete this.clear;
+    delete this.set;
+    delete this.editRange;
+  }
+
+  /** Returns true if the tree appears to be frozen. */
+  get isFrozen() {
+    return this.hasOwnProperty('editRange');
+  }
+
+  /** Scans the tree for signs of serious bugs (e.g. this.size doesn't match
+   *  number of elements, internal nodes not caching max element properly...)
+   *  Computational complexity: O(number of nodes), i.e. O(size). This method
+   *  skips the most expensive test - whether all keys are sorted - but it
+   *  does check that maxKey() of the children of internal nodes are sorted. */
+  checkValid() {
+    var size = this._root.checkValid(0, this);
+    check(size === this.size, "size mismatch: counted ", size, "but stored", this.size);
+  }
+}
+
+declare const Symbol: any;
+if (Symbol && Symbol.iterator) // iterator is equivalent to entries()
+  (BTree as any).prototype[Symbol.iterator] = BTree.prototype.entries;
+(BTree as any).prototype.where = BTree.prototype.filter;
+(BTree as any).prototype.setRange = BTree.prototype.setPairs;
+(BTree as any).prototype.add = BTree.prototype.set;
+
+function iterator<T>(next: () => {done:boolean,value?:T} = (() => ({ done:true, value:undefined }))): IterableIterator<T> {
+  var result: any = { next };
+  if (Symbol && Symbol.iterator)
+    result[Symbol.iterator] = function() { return this; };
+  return result;
+}
+  
+
+/** Leaf node / base class. **************************************************/
+class BNode<K,V> {
+  // If this is an internal node, _keys[i] is the highest key in children[i].
+  keys: K[];
+  values: V[];
+  isShared: true | undefined;
+  get isLeaf() { return (this as any).children === undefined; }
+  
+  constructor(keys: K[] = [], values?: V[]) {
+    this.keys = keys;
+    this.values = values || undefVals as any[];
+    this.isShared = undefined;
+  }
+
+  // Shared methods /////////////////////////////////////////////////////////
+
+  maxKey() {
+    return this.keys[this.keys.length-1];
+  }
+
+  // If key not found, returns i^failXor where i is the insertion index.
+  // Callers that don't care whether there was a match will set failXor=0.
+  indexOf(key: K, failXor: number, cmp: (a:K, b:K) => number): index {
+    // TODO: benchmark multiple search strategies
+    const keys = this.keys;
+    var lo = 0, hi = keys.length, mid = hi >> 1;
+    while(lo < hi) {
+      var c = cmp(keys[mid], key);
+      if (c < 0)
+        lo = mid + 1;
+      else if (c > 0) // key < keys[mid]
+        hi = mid;
+      else if (c === 0)
+        return mid;
+      else {
+        // c is NaN or otherwise invalid
+        if (key === key) // at least the search key is not NaN
+          return keys.length;
+        else
+          throw new Error("BTree: NaN was used as a key");
+      }
+      mid = (lo + hi) >> 1;
+    }
+    return mid ^ failXor;
+
+    // Unrolled version: benchmarks show same speed, not worth using
+    /*var i = 1, c: number = 0, sum = 0;
+    if (keys.length >= 4) {
+      i = 3;
+      if (keys.length >= 8) {
+        i = 7;
+        if (keys.length >= 16) {
+          i = 15;
+          if (keys.length >= 32) {
+            i = 31;
+            if (keys.length >= 64) {
+              i = 127;
+              i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 64 : -64;
+              sum += c;
+              i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 32 : -32;
+              sum += c;
+            }
+            i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 16 : -16;
+            sum += c;
+          }
+          i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 8 : -8;
+          sum += c;
+        }
+        i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 4 : -4;
+        sum += c;
+      }
+      i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 2 : -2;
+      sum += c;
+    }
+    i += (c = i < keys.length ? cmp(keys[i], key) : 1) < 0 ? 1 : -1;
+    c = i < keys.length ? cmp(keys[i], key) : 1;
+    sum += c;
+    if (c < 0) {
+      ++i;
+      c = i < keys.length ? cmp(keys[i], key) : 1;
+      sum += c;
+    }
+    if (sum !== sum) {
+      if (key === key) // at least the search key is not NaN
+        return keys.length ^ failXor;
+      else
+        throw new Error("BTree: NaN was used as a key");
+    }
+    return c === 0 ? i : i ^ failXor;*/
+  }
+
+  // Leaf Node: misc //////////////////////////////////////////////////////////
+
+  minKey() {
+    return this.keys[0];
+  }
+
+  clone(): BNode<K,V> {
+    var v = this.values;
+    return new BNode<K,V>(this.keys.slice(0), v === undefVals ? v : v.slice(0));
+  }
+
+  greedyClone(force?: boolean): BNode<K,V> {
+    return this.isShared && !force ? this : this.clone();
+  }
+
+  get(key: K, defaultValue: V|undefined, tree: BTree<K,V>): V|undefined {
+    var i = this.indexOf(key, -1, tree._compare);
+    return i < 0 ? defaultValue : this.values[i];
+  }
+
+  checkValid(depth: number, tree: BTree<K,V>): number {
+    var kL = this.keys.length, vL = this.values.length;
+    check(this.values === undefVals ? kL <= vL : kL === vL,
+      "keys/values length mismatch: depth", depth, "with lengths", kL, vL);
+    // Note: we don't check for "node too small" because sometimes a node
+    // can legitimately have size 1. This occurs if there is a batch 
+    // deletion, leaving a node of size 1, and the siblings are full so
+    // it can't be merged with adjacent nodes. However, the parent will
+    // verify that the average node size is at least half of the maximum.
+    check(depth == 0 || kL > 0, "empty leaf at depth", depth);
+    return kL;
+  }
+
+  // Leaf Node: set & node splitting //////////////////////////////////////////
+
+  set(key: K, value: V, overwrite: boolean|undefined, tree: BTree<K,V>): boolean|BNode<K,V> { 
+    var i = this.indexOf(key, -1, tree._compare);
+    if (i < 0) {
+      // key does not exist yet
+      i = ~i;
+      tree._size++;
+      
+      if (this.keys.length < tree._maxNodeSize) {
+        return this.insertInLeaf(i, key, value, tree);
+      } else {
+        // This leaf node is full and must split
+        var newRightSibling = this.splitOffRightSide(), target: BNode<K,V> = this;
+        if (i > this.keys.length) {
+          i -= this.keys.length;
+          target = newRightSibling;
+        }
+        target.insertInLeaf(i, key, value, tree);
+        return newRightSibling;
+      }
+    } else {
+      // Key already exists
+      if (overwrite !== false) {
+        if (value !== undefined)
+          this.reifyValues();
+        // usually this is a no-op, but some users may wish to edit the key
+        this.keys[i] = key;
+        this.values[i] = value;
+      }
+      return false;
+    }
+  }
+
+  reifyValues() {
+    if (this.values === undefVals)
+      return this.values = this.values.slice(0, this.keys.length);
+    return this.values;
+  }
+
+  insertInLeaf(i: index, key: K, value: V, tree: BTree<K,V>) {
+    this.keys.splice(i, 0, key);
+    if (this.values === undefVals) {
+      while (undefVals.length < tree._maxNodeSize)
+        undefVals.push(undefined);
+      if (value === undefined) {
+        return true;
+      } else {
+        this.values = undefVals.slice(0, this.keys.length - 1);
+      }
+    }
+    this.values.splice(i, 0, value);
+    return true;
+  }
+  
+  takeFromRight(rhs: BNode<K,V>) {
+    // Reminder: parent node must update its copy of key for this node
+    // assert: neither node is shared
+    // assert rhs.keys.length > (maxNodeSize/2 && this.keys.length<maxNodeSize)
+    var v = this.values;
+    if (rhs.values === undefVals) {
+      if (v !== undefVals)
+        v.push(undefined as any);
+    } else {
+      v = this.reifyValues();
+      v.push(rhs.values.shift()!);
+    }
+    this.keys.push(rhs.keys.shift()!);
+  }
+
+  takeFromLeft(lhs: BNode<K,V>) {
+    // Reminder: parent node must update its copy of key for this node
+    // assert: neither node is shared
+    // assert rhs.keys.length > (maxNodeSize/2 && this.keys.length<maxNodeSize)
+    var v = this.values;
+    if (lhs.values === undefVals) {
+      if (v !== undefVals)
+        v.unshift(undefined as any);
+    } else {
+      v = this.reifyValues();
+      v.unshift(lhs.values.pop()!);
+    }
+    this.keys.unshift(lhs.keys.pop()!);
+  }
+
+  splitOffRightSide(): BNode<K,V> {
+    // Reminder: parent node must update its copy of key for this node
+    var half = this.keys.length >> 1, keys = this.keys.splice(half);
+    var values = this.values === undefVals ? undefVals : this.values.splice(half);
+    return new BNode<K,V>(keys, values);
+  }
+
+  // Leaf Node: scanning & deletions //////////////////////////////////////////
+
+  forRange<R>(low: K, high: K, includeHigh: boolean|undefined, editMode: boolean, tree: BTree<K,V>, count: number,
+              onFound?: (k:K, v:V, counter:number) => EditRangeResult<V,R>|void): EditRangeResult<V,R>|number {
+    var cmp = tree._compare;
+    var iLow, iHigh;
+    if (high === low) {
+      if (!includeHigh)
+        return count;
+      iHigh = (iLow = this.indexOf(low, -1, cmp)) + 1;
+      if (iLow < 0)
+        return count;
+    } else {
+      iLow = this.indexOf(low, 0, cmp);
+      iHigh = this.indexOf(high, -1, cmp);
+      if (iHigh < 0)
+        iHigh = ~iHigh;
+      else if (includeHigh === true)
+        iHigh++;
+    }
+    var keys = this.keys, values = this.values;
+    if (onFound !== undefined) {
+      for(var i = iLow; i < iHigh; i++) {
+        var key = keys[i];
+        var result = onFound(key, values[i], count++);
+        if (result !== undefined) {
+          if (editMode === true) {
+            if (key !== keys[i] || this.isShared === true)
+              throw new Error("BTree illegally changed or cloned in editRange");
+            if (result.delete) {
+              this.keys.splice(i, 1);
+              if (this.values !== undefVals)
+                this.values.splice(i, 1);
+              tree._size--;
+              i--;
+              iHigh--;
+            } else if (result.hasOwnProperty('value')) {
+              values![i] = result.value!;
+            }
+          }
+          if (result.break !== undefined)
+            return result;
+        }
+      }
+    } else
+      count += iHigh - iLow;
+    return count;
+  }
+
+  /** Adds entire contents of right-hand sibling (rhs is left unchanged) */
+  mergeSibling(rhs: BNode<K,V>, _: number) {
+    this.keys.push.apply(this.keys, rhs.keys);
+    if (this.values === undefVals) {
+      if (rhs.values === undefVals)
+        return;
+      this.values = this.values.slice(0, this.keys.length);
+    }
+    this.values.push.apply(this.values, rhs.reifyValues());
+  }
+}
+
+/** Internal node (non-leaf node) ********************************************/
+class BNodeInternal<K,V> extends BNode<K,V> {
+  // Note: conventionally B+ trees have one fewer key than the number of 
+  // children, but I find it easier to keep the array lengths equal: each
+  // keys[i] caches the value of children[i].maxKey().
+  children: BNode<K,V>[];
+
+  constructor(children: BNode<K,V>[], keys?: K[]) {
+    if (!keys) {
+      keys = [];
+      for (var i = 0; i < children.length; i++)
+        keys[i] = children[i].maxKey();
+    }
+    super(keys);
+    this.children = children;
+  }
+
+  clone(): BNode<K,V> {
+    var children = this.children.slice(0);
+    for (var i = 0; i < children.length; i++)
+      children[i].isShared = true;
+    return new BNodeInternal<K,V>(children, this.keys.slice(0));
+  }
+
+  greedyClone(force?: boolean): BNode<K,V> {
+    if (this.isShared && !force)
+      return this;
+    var nu = new BNodeInternal<K,V>(this.children.slice(0), this.keys.slice(0));
+    for (var i = 0; i < nu.children.length; i++)
+      nu.children[i] = nu.children[i].greedyClone();
+    return nu;
+  }
+
+  minKey() {
+    return this.children[0].minKey();
+  }
+
+  get(key: K, defaultValue: V|undefined, tree: BTree<K,V>): V|undefined {
+    var i = this.indexOf(key, 0, tree._compare), children = this.children;
+    return i < children.length ? children[i].get(key, defaultValue, tree) : undefined;
+  }
+
+  checkValid(depth: number, tree: BTree<K,V>) : number {
+    var kL = this.keys.length, cL = this.children.length;
+    check(kL === cL, "keys/children length mismatch: depth", depth, "lengths", kL, cL);
+    check(kL > 1, "internal node has length", kL, "at depth", depth);
+    var size = 0, c = this.children, k = this.keys, childSize = 0;
+    for (var i = 0; i < cL; i++) {
+      size += c[i].checkValid(depth + 1, tree);
+      childSize += c[i].keys.length;
+      check(size >= childSize, "wtf"); // no way this will ever fail
+      check(i === 0 || c[i-1].constructor === c[i].constructor, "type mismatch");
+      if (c[i].maxKey() != k[i])
+        check(false, "keys[", i, "] =", k[i], "is wrong, should be ", c[i].maxKey(), "at depth", depth);
+      if (!(i === 0 || tree._compare(k[i-1], k[i]) < 0))
+        check(false, "sort violation at depth", depth, "index", i, "keys", k[i-1], k[i]);
+    }
+    var toofew = childSize < (tree.maxNodeSize >> 1)*cL;
+    if (toofew || childSize > tree.maxNodeSize*cL)
+      check(false, toofew ? "too few" : "too many", "children (", childSize, size, ") at depth", depth, ", maxNodeSize:", tree.maxNodeSize, "children.length:", cL);
+    return size;
+  }
+
+  // Internal Node: set & node splitting //////////////////////////////////////
+
+  set(key: K, value: V, overwrite: boolean|undefined, tree: BTree<K,V>): boolean|BNodeInternal<K,V> {
+    var c = this.children, max = tree._maxNodeSize, cmp = tree._compare;
+    var i = Math.min(this.indexOf(key, 0, cmp), c.length - 1), child = c[i];
+    
+    if (child.isShared)
+      c[i] = child = child.clone();
+    if (child.keys.length >= max) {
+      // child is full; inserting anything else will cause a split.
+      // Shifting an item to the left or right sibling may avoid a split.
+      // We can do a shift if the adjacent node is not full and if the
+      // current key can still be placed in the same node after the shift.
+      var other: BNode<K,V>;
+      if (i > 0 && (other = c[i-1]).keys.length < max && cmp(child.keys[0], key) < 0) {
+        if (other.isShared)
+          c[i-1] = other = other.clone();
+        other.takeFromRight(child);
+        this.keys[i-1] = other.maxKey();
+      } else if ((other = c[i+1]) !== undefined && other.keys.length < max && cmp(child.maxKey(), key) < 0) {
+        if (other.isShared)
+          c[i+1] = other = other.clone();
+        other.takeFromLeft(child);
+        this.keys[i] = c[i].maxKey();
+      }
+    }
+
+    var result = child.set(key, value, overwrite, tree);
+    if (result === false)
+      return false;
+    this.keys[i] = child.maxKey();
+    if (result === true)
+      return true;
+
+    // The child has split and `result` is a new right child... does it fit?
+    if (this.keys.length < max) { // yes
+      this.insert(i+1, result);
+      return true;
+    } else { // no, we must split also
+      var newRightSibling = this.splitOffRightSide(), target: BNodeInternal<K,V> = this;
+      if (cmp(result.maxKey(), this.maxKey()) > 0) {
+        target = newRightSibling;
+        i -= this.keys.length;
+      }
+      target.insert(i+1, result);
+      return newRightSibling;
+    }
+  }
+
+  insert(i: index, child: BNode<K,V>) {
+    this.children.splice(i, 0, child);
+    this.keys.splice(i, 0, child.maxKey());
+  }
+
+  splitOffRightSide() {
+    var half = this.children.length >> 1;
+    return new BNodeInternal<K,V>(this.children.splice(half), this.keys.splice(half));
+  }
+
+  takeFromRight(rhs: BNode<K,V>) {
+    // Reminder: parent node must update its copy of key for this node
+    // assert: neither node is shared
+    // assert rhs.keys.length > (maxNodeSize/2 && this.keys.length<maxNodeSize)
+    this.keys.push(rhs.keys.shift()!);
+    this.children.push((rhs as BNodeInternal<K,V>).children.shift()!);
+  }
+
+  takeFromLeft(lhs: BNode<K,V>) {
+    // Reminder: parent node must update its copy of key for this node
+    // assert: neither node is shared
+    // assert rhs.keys.length > (maxNodeSize/2 && this.keys.length<maxNodeSize)
+    this.keys.unshift(lhs.keys.pop()!);
+    this.children.unshift((lhs as BNodeInternal<K,V>).children.pop()!);
+  }
+
+  // Internal Node: scanning & deletions //////////////////////////////////////
+
+  forRange<R>(low: K, high: K, includeHigh: boolean|undefined, editMode: boolean, tree: BTree<K,V>, count: number,
+    onFound?: (k:K, v:V, counter:number) => EditRangeResult<V,R>|void): EditRangeResult<V,R>|number
+  {
+    var cmp = tree._compare;
+    var iLow = this.indexOf(low, 0, cmp), i = iLow;
+    var iHigh = Math.min(high === low ? iLow : this.indexOf(high, 0, cmp), this.keys.length-1);
+    var keys = this.keys, children = this.children;
+    if (!editMode) {
+      // Simple case
+      for(; i <= iHigh; i++) {
+        var result = children[i].forRange(low, high, includeHigh, editMode, tree, count, onFound);
+        if (typeof result !== 'number')
+          return result;
+        count = result;
+      }
+    } else if (i <= iHigh) {
+      try {
+        for(; i <= iHigh; i++) {
+          if (children[i].isShared)
+            children[i] = children[i].clone();
+          var result = children[i].forRange(low, high, includeHigh, editMode, tree, count, onFound);
+          keys[i] = children[i].maxKey();
+          if (typeof result !== 'number')
+            return result;
+          count = result;
+        }
+      } finally {
+        // Deletions may have occurred, so look for opportunities to merge nodes.
+        var half = tree._maxNodeSize >> 1;
+        if (iLow > 0)
+          iLow--;
+        for(i = iHigh; i >= iLow; i--) {
+          if (children[i].keys.length <= half)
+            this.tryMerge(i, tree._maxNodeSize);
+        }
+        // Are we completely empty?
+        if (children[0].keys.length === 0) {
+          check(children.length === 1 && keys.length === 1, "emptiness bug");
+          children.shift();
+          keys.shift();
+        }
+      }
+    }
+    return count;
+  }
+
+  /** Merges child i with child i+1 if their combined size is not too large */
+  tryMerge(i: index, maxSize: number): boolean {
+    var children = this.children;
+    if (i >= 0 && i + 1 < children.length) {
+      if (children[i].keys.length + children[i+1].keys.length <= maxSize) {
+        if (children[i].isShared) // cloned already UNLESS i is outside scan range
+          children[i] = children[i].clone();
+        children[i].mergeSibling(children[i+1], maxSize);
+        children.splice(i + 1, 1);
+        this.keys.splice(i + 1, 1);
+        this.keys[i] = children[i].maxKey();
+        return true;
+      }
+    }
+    return false;
+  }
+
+  mergeSibling(rhs: BNode<K,V>, maxNodeSize: number) {
+    // assert !this.isShared;
+    var oldLength = this.keys.length;
+    this.keys.push.apply(this.keys, rhs.keys);
+    this.children.push.apply(this.children, (rhs as any as BNodeInternal<K,V>).children);
+    // If our children are themselves almost empty due to a mass-delete,
+    // they may need to be merged too (but only the oldLength-1 and its
+    // right sibling should need this).
+    this.tryMerge(oldLength-1, maxNodeSize);
+  }
+}
+
+// Optimization: this array of `undefined`s is used instead of a normal
+// array of values in nodes where `undefined` is the only value.
+// Its length is extended to max node size on first use; since it can
+// be shared between trees with different maximums, its length can only
+// increase, never decrease. Its type should be undefined[] but strangely
+// TypeScript won't allow the comparison V[] === undefined[]. To prevent
+// users from making this array too large, BTree has a maximum node size.
+var undefVals: any[] = [];
+
+const Delete = {delete: true}, DeleteRange = () => Delete;
+const Break = {break: true};
+const EmptyLeaf = (function() { 
+  var n = new BNode<any,any>(); n.isShared = true; return n;
+})();
+const EmptyArray: any[] = [];
+const ReusedArray: any[] = []; // assumed thread-local
+
+function check(fact: boolean, ...args: any[]) {
+  if (!fact) {
+    args.unshift('B+ tree '); // at beginning of message
+    throw new Error(args.join(' '));
+  }
+}
+
+/** A BTree frozen in the empty state. */
+export const EmptyBTree = (() => { let t = new BTree(); t.freeze(); return t; })();
\ No newline at end of file
diff --git a/packages/idb-bridge/src/tree/interfaces.ts b/packages/idb-bridge/src/tree/interfaces.ts
new file mode 100644
index 000000000..c708c20b5
--- /dev/null
+++ b/packages/idb-bridge/src/tree/interfaces.ts
@@ -0,0 +1,329 @@
+/*
+Copyright (c) 2018 David Piepgrass
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+SPDX-License-Identifier: MIT
+*/
+
+// Original repository: https://github.com/qwertie/btree-typescript
+
+
+/** Read-only set interface (subinterface of IMapSource<K,any>).
+ *  The word "set" usually means that each item in the collection is unique
+ *  (appears only once, based on a definition of equality used by the 
+ *  collection.) Objects conforming to this interface aren't guaranteed not 
+ *  to contain duplicates, but as an example, BTree<K,V> implements this 
+ *  interface and does not allow duplicates. */
+export interface ISetSource<K=any>
+{
+  /** Returns the number of key/value pairs in the map object. */
+  size: number;
+  /** Returns a boolean asserting whether the key exists in the map object or not. */
+  has(key: K): boolean;
+  /** Returns a new iterator for iterating the items in the set (the order is implementation-dependent). */
+  keys(): IterableIterator<K>;
+}
+
+/** Read-only map interface (i.e. a source of key-value pairs). */
+export interface IMapSource<K=any, V=any> extends ISetSource<K>
+{
+  /** Returns the number of key/value pairs in the map object. */
+  size: number;
+  /** Returns the value associated to the key, or undefined if there is none. */
+  get(key: K): V|undefined;
+  /** Returns a boolean asserting whether the key exists in the map object or not. */
+  has(key: K): boolean;
+  /** Calls callbackFn once for each key-value pair present in the map object.
+   *  The ES6 Map class sends the value to the callback before the key, so
+   *  this interface must do likewise. */
+  forEach(callbackFn: (v:V, k:K, map:IMapSource<K,V>) => void, thisArg: any): void;
+  
+  /** Returns an iterator that provides all key-value pairs from the collection (as arrays of length 2). */
+  entries(): IterableIterator<[K,V]>;
+  /** Returns a new iterator for iterating the keys of each pair. */
+  keys(): IterableIterator<K>;
+  /** Returns a new iterator for iterating the values of each pair. */
+  values(): IterableIterator<V>;
+  // TypeScript compiler decided Symbol.iterator has type 'any'
+  //[Symbol.iterator](): IterableIterator<[K,V]>;
+}
+
+/** Write-only set interface (the set cannot be queried, but items can be added to it.) 
+ *  @description Note: BTree<K,V> does not officially implement this interface,
+ *               but BTree<K> can be used as an instance of ISetSink<K>. */
+export interface ISetSink<K=any>
+{
+  /** Adds the specified item to the set, if it was not in the set already. */
+  add(key: K): any;
+  /** Returns true if an element in the map object existed and has been 
+   *  removed, or false if the element did not exist. */
+  delete(key: K): boolean;
+  /** Removes everything so that the set is empty. */
+  clear(): void;
+}
+
+/** Write-only map interface (i.e. a drain into which key-value pairs can be "sunk") */
+export interface IMapSink<K=any, V=any>
+{
+  /** Returns true if an element in the map object existed and has been 
+   *  removed, or false if the element did not exist. */
+  delete(key: K): boolean;
+  /** Sets the value for the key in the map object (the return value is 
+   *  boolean in BTree but Map returns the Map itself.) */
+  set(key: K, value: V): any;
+  /** Removes all key/value pairs from the IMap object. */
+  clear(): void;
+}
+
+/** Set interface.
+ *  @description Note: BTree<K,V> does not officially implement this interface,
+ *               but BTree<K> can be used as an instance of ISet<K>. */
+export interface ISet<K=any> extends ISetSource<K>, ISetSink<K> { }
+
+/** An interface compatible with ES6 Map and BTree. This interface does not
+ *  describe the complete interface of either class, but merely the common 
+ *  interface shared by both. */
+export interface IMap<K=any, V=any> extends IMapSource<K, V>, IMapSink<K, V> { }
+
+/** An data source that provides read-only access to a set of items called
+ *  "keys" in sorted order. This is a subinterface of ISortedMapSource. */
+export interface ISortedSetSource<K=any> extends ISetSource<K>
+{
+  /** Gets the lowest key in the collection. */
+  minKey(): K | undefined;
+  /** Gets the highest key in the collection. */
+  maxKey(): K | undefined;
+  /** Returns the next key larger than the specified key (or undefined if there is none) */
+  nextHigherKey(key: K): K|undefined;
+  /** Returns the next key smaller than the specified key (or undefined if there is none) */
+  nextLowerKey(key: K): K|undefined;
+  /** Calls `callback` on the specified range of keys, in ascending order by key.
+   * @param low The first key scanned will be greater than or equal to `low`.
+   * @param high Scanning stops when a key larger than this is reached.
+   * @param includeHigh If the `high` key is present in the map, `onFound` is called 
+   *        for that final pair if and only if this parameter is true.
+   * @param onFound A function that is called for each key pair. Because this
+   *        is a subinterface of ISortedMapSource, if there is a value 
+   *        associated with the key, it is passed as the second parameter.
+   * @param initialCounter Initial third argument of `onFound`. This value 
+   *        increases by one each time `onFound` is called. Default: 0
+   * @returns Number of pairs found and the number of times `onFound` was called.
+   */
+  forRange(low: K, high: K, includeHigh: boolean, onFound?: (k:K,v:any,counter:number) => void, initialCounter?: number): number;
+  /** Returns a new iterator for iterating the keys of each pair in ascending order. 
+   *  @param firstKey: Minimum key to include in the output. */
+  keys(firstKey?: K): IterableIterator<K>;
+}
+
+/** An data source that provides read-only access to items in sorted order. */
+export interface ISortedMapSource<K=any, V=any> extends IMapSource<K, V>, ISortedSetSource<K>
+{
+  /** Returns the next pair whose key is larger than the specified key (or undefined if there is none) */
+  nextHigherPair(key: K): [K,V]|undefined;
+  /** Returns the next pair whose key is smaller than the specified key (or undefined if there is none) */
+  nextLowerPair(key: K): [K,V]|undefined;
+  /** Builds an array of pairs from the specified range of keys, sorted by key.
+   * Each returned pair is also an array: pair[0] is the key, pair[1] is the value.
+   * @param low The first key in the array will be greater than or equal to `low`.
+   * @param high This method returns when a key larger than this is reached.
+   * @param includeHigh If the `high` key is present in the map, its pair will be
+   *        included in the output if and only if this parameter is true. Note: 
+   *        if the `low` key is present, it is always included in the output.
+   * @param maxLength Maximum length of the returned array (default: unlimited)
+   * @description Computational complexity: O(result.length + log size)
+   */
+  getRange(low: K, high: K, includeHigh?: boolean, maxLength?: number): [K,V][];
+  /** Calls `callback` on the specified range of keys, in ascending order by key.
+   * @param low The first key scanned will be greater than or equal to `low`.
+   * @param high Scanning stops when a key larger than this is reached.
+   * @param includeHigh If the `high` key is present in the map, `onFound` is called 
+   *        for that final pair if and only if this parameter is true.
+   * @param onFound A function that is called for each key-value pair.
+   * @param initialCounter Initial third argument of onFound. This value 
+   *        increases by one each time `onFound` is called. Default: 0
+   * @returns Number of pairs found and the number of times `callback` was called.
+   */
+  forRange(low: K, high: K, includeHigh: boolean, onFound?: (k:K,v:V,counter:number) => void, initialCounter?: number): number;
+  /** Returns an iterator that provides items in order by key.
+   *  @param firstKey: Minimum key to include in the output. */
+  entries(firstKey?: K): IterableIterator<[K,V]>;
+  /** Returns a new iterator for iterating the keys of each pair in ascending order. 
+   *  @param firstKey: Minimum key to include in the output. */
+  keys(firstKey?: K): IterableIterator<K>;
+  /** Returns a new iterator for iterating the values of each pair in order by key. 
+   *  @param firstKey: Minimum key whose associated value is included in the output. */
+  values(firstKey?: K): IterableIterator<V>;
+  
+  // This method should logically be in IMapSource but is not supported by ES6 Map
+  /** Performs a reduce operation like the `reduce` method of `Array`. 
+   *  It is used to combine all pairs into a single value, or perform conversions. */
+  reduce<R>(callback: (previous:R,currentPair:[K,V],counter:number,tree:IMapF<K,V>) => R, initialValue: R): R;
+  /** Performs a reduce operation like the `reduce` method of `Array`. 
+   *  It is used to combine all pairs into a single value, or perform conversions. */
+  reduce<R>(callback: (previous:R|undefined,currentPair:[K,V],counter:number,tree:IMapF<K,V>) => R): R|undefined;
+}
+
+/** An interface for a set of keys (the combination of ISortedSetSource<K> and ISetSink<K>) */
+export interface ISortedSet<K=any> extends ISortedSetSource<K>, ISetSink<K> { }
+
+/** An interface for a sorted map (dictionary), 
+ *  not including functional/persistent methods. */
+export interface ISortedMap<K=any, V=any> extends IMap<K,V>, ISortedMapSource<K, V>
+{
+  // All of the following methods should be in IMap but are left out of IMap
+  // so that IMap is compatible with ES6 Map.
+
+  /** Adds or overwrites a key-value pair in the sorted map.
+   * @param key the key is used to determine the sort order of data in the tree.
+   * @param value data to associate with the key
+   * @param overwrite Whether to overwrite an existing key-value pair 
+   *        (default: true). If this is false and there is an existing
+   *        key-value pair then the call to this method has no effect.
+   * @returns true if a new key-value pair was added, false if the key 
+   *        already existed. */
+  set(key: K, value: V, overwrite?: boolean): boolean;
+  /** Adds all pairs from a list of key-value pairs.
+   * @param pairs Pairs to add to this tree. If there are duplicate keys, 
+   *        later pairs currently overwrite earlier ones (e.g. [[0,1],[0,7]] 
+   *        associates 0 with 7.)
+   * @param overwrite Whether to overwrite pairs that already exist (if false,
+   *        pairs[i] is ignored when the key pairs[i][0] already exists.)
+   * @returns The number of pairs added to the collection.
+   */
+  setPairs(pairs: [K,V][], overwrite?: boolean): number;
+  /** Deletes a series of keys from the collection. */
+  deleteKeys(keys: K[]): number;
+  /** Removes a range of key-value pairs from the B+ tree.
+   * @param low The first key deleted will be greater than or equal to `low`.
+   * @param high Deleting stops when a key larger than this is reached.
+   * @param includeHigh Specifies whether the `high` key, if present, is deleted.
+   * @returns The number of key-value pairs that were deleted. */
+  deleteRange(low: K, high: K, includeHigh: boolean): number;
+
+  // TypeScript requires these methods of ISortedMapSource to be repeated
+  entries(firstKey?: K): IterableIterator<[K,V]>;
+  keys(firstKey?: K): IterableIterator<K>;
+  values(firstKey?: K): IterableIterator<V>;
+}
+
+/** An interface for a functional set, in which the set object could be read-only 
+ *  but new versions of the set can be created by calling "with" or "without" 
+ *  methods to add or remove keys. This is a subinterface of IMapF<K,V>,
+ *  so the items in the set may be referred to as "keys". */
+export interface ISetF<K=any> extends ISetSource<K> {
+  /** Returns a copy of the set with the specified key included. 
+   *  @description You might wonder why this method accepts only one key 
+   *  instead of `...keys: K[]`. The reason is that the derived interface
+   *  IMapF expects the second parameter to be a value. Therefore
+   *  withKeys() is provided to set multiple keys at once. */
+  with(key: K): ISetF<K>;
+  /** Returns a copy of the set with the specified key removed. */
+  without(key: K): ISetF<K>;
+  /** Returns a copy of the tree with all the keys in the specified array present.
+   *  @param keys The keys to add.
+   *  @param returnThisIfUnchanged If true, the method returns `this` when
+   *         all of the keys are already present in the collection. The 
+   *         default value may be true or false depending on the concrete
+   *         implementation of the interface (in BTree, the default is false.) */
+  withKeys(keys: K[], returnThisIfUnchanged?: boolean): ISetF<K>;
+  /** Returns a copy of the tree with all the keys in the specified array removed. */
+  withoutKeys(keys: K[], returnThisIfUnchanged?: boolean): ISetF<K>;
+  /** Returns a copy of the tree with items removed whenever the callback 
+   *  function returns false.
+   *  @param callback A function to call for each item in the set.
+   *         The second parameter to `callback` exists because ISetF
+   *         is a subinterface of IMapF. If the object is a map, v
+   *         is the value associated with the key, otherwise v could be
+   *         undefined or another copy of the third parameter (counter). */
+  filter(callback: (k:K,v:any,counter:number) => boolean, returnThisIfUnchanged?: boolean): ISetF<K>;
+}
+
+/** An interface for a functional map, in which the map object could be read-only
+ *  but new versions of the map can be created by calling "with" or "without" 
+ *  methods to add or remove keys or key-value pairs. 
+ */
+export interface IMapF<K=any, V=any> extends IMapSource<K, V>, ISetF<K> {
+  /** Returns a copy of the tree with the specified key set (the value is undefined). */
+  with(key: K): IMapF<K,V|undefined>;
+  /** Returns a copy of the tree with the specified key-value pair set. */
+  with<V2>(key: K, value: V2, overwrite?: boolean): IMapF<K,V|V2>;
+  /** Returns a copy of the tree with the specified key-value pairs set. */
+  withPairs<V2>(pairs: [K,V|V2][], overwrite: boolean): IMapF<K,V|V2>;
+  /** Returns a copy of the tree with all the keys in the specified array present.
+   *  @param keys The keys to add. If a key is already present in the tree,
+   *         neither the existing key nor the existing value is modified. 
+   *  @param returnThisIfUnchanged If true, the method returns `this` when
+   *         all of the keys are already present in the collection. The 
+   *         default value may be true or false depending on the concrete
+   *         implementation of the interface (in BTree, the default is false.) */
+  withKeys(keys: K[], returnThisIfUnchanged?: boolean): IMapF<K,V|undefined>;
+  /** Returns a copy of the tree with all values altered by a callback function. */
+  mapValues<R>(callback: (v:V,k:K,counter:number) => R): IMapF<K,R>;
+  /** Performs a reduce operation like the `reduce` method of `Array`. 
+   *  It is used to combine all pairs into a single value, or perform conversions. */
+  reduce<R>(callback: (previous:R,currentPair:[K,V],counter:number,tree:IMapF<K,V>) => R, initialValue: R): R;
+  /** Performs a reduce operation like the `reduce` method of `Array`. 
+   *  It is used to combine all pairs into a single value, or perform conversions. */
+  reduce<R>(callback: (previous:R|undefined,currentPair:[K,V],counter:number,tree:IMapF<K,V>) => R): R|undefined;
+
+  // Update return types in ISetF
+  without(key: K): IMapF<K,V>;
+  withoutKeys(keys: K[], returnThisIfUnchanged?: boolean): IMapF<K,V>;
+  /** Returns a copy of the tree with pairs removed whenever the callback 
+   *  function returns false. */
+  filter(callback: (k:K,v:V,counter:number) => boolean, returnThisIfUnchanged?: boolean): IMapF<K,V>;
+}
+
+/** An interface for a functional sorted set: a functional set in which the 
+ *  keys (items) are sorted. This is a subinterface of ISortedMapF. */
+export interface ISortedSetF<K=any> extends ISetF<K>, ISortedSetSource<K>
+{
+  // TypeScript requires this method of ISortedSetSource to be repeated
+  keys(firstKey?: K): IterableIterator<K>;
+}
+
+export interface ISortedMapF<K=any,V=any> extends ISortedSetF<K>, IMapF<K,V>, ISortedMapSource<K,V>
+{
+  /** Returns a copy of the tree with the specified range of keys removed. */
+  withoutRange(low: K, high: K, includeHigh: boolean, returnThisIfUnchanged?: boolean): ISortedMapF<K,V>;
+
+  // TypeScript requires these methods of ISortedSetF and ISortedMapSource to be repeated
+  entries(firstKey?: K): IterableIterator<[K,V]>;
+  keys(firstKey?: K): IterableIterator<K>;
+  values(firstKey?: K): IterableIterator<V>;
+  forRange(low: K, high: K, includeHigh: boolean, onFound?: (k:K,v:V,counter:number) => void, initialCounter?: number): number;
+
+  // Update the return value of methods from base interfaces
+  with(key: K): ISortedMapF<K,V|undefined>;
+  with<V2>(key: K, value: V2, overwrite?: boolean): ISortedMapF<K,V|V2>;
+  withKeys(keys: K[], returnThisIfUnchanged?: boolean): ISortedMapF<K,V|undefined>;
+  withPairs<V2>(pairs: [K,V|V2][], overwrite: boolean): ISortedMapF<K,V|V2>;
+  mapValues<R>(callback: (v:V,k:K,counter:number) => R): ISortedMapF<K,R>;
+  without(key: K): ISortedMapF<K,V>;
+  withoutKeys(keys: K[], returnThisIfUnchanged?: boolean): ISortedMapF<K,V>;
+  filter(callback: (k:K,v:any,counter:number) => boolean, returnThisIfUnchanged?: boolean): ISortedMapF<K,V>;
+}
+
+export interface ISortedMapConstructor<K,V> {
+    new (entries?: [K,V][], compare?: (a: K, b: K) => number): ISortedMap<K,V>;
+}
+export interface ISortedMapFConstructor<K,V> {
+    new (entries?: [K,V][], compare?: (a: K, b: K) => number): ISortedMapF<K,V>;
+}
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