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diff --git a/contexts/data/lib/closure-library/closure/goog/structs/priorityqueue.js b/contexts/data/lib/closure-library/closure/goog/structs/priorityqueue.js
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+// Copyright 2006 The Closure Library Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS-IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/**
+ * @fileoverview Datastructure: Priority Queue.
+ *
+ *
+ * This file provides the implementation of a Priority Queue. Smaller priorities
+ * move to the front of the queue. If two values have the same priority,
+ * it is arbitrary which value will come to the front of the queue first.
+ */
+
+// TODO(user): Should this rely on natural ordering via some Comparable
+//     interface?
+
+
+goog.provide('goog.structs.PriorityQueue');
+
+goog.require('goog.structs');
+goog.require('goog.structs.Heap');
+
+
+
+/**
+ * Class for Priority Queue datastructure.
+ *
+ * @constructor
+ * @extends {goog.structs.Heap}
+ */
+goog.structs.PriorityQueue = function() {
+  goog.structs.Heap.call(this);
+};
+goog.inherits(goog.structs.PriorityQueue, goog.structs.Heap);
+
+
+/**
+ * Puts the specified value in the queue.
+ * @param {*} priority The priority of the value.
+ * @param {*} value The value.
+ */
+goog.structs.PriorityQueue.prototype.enqueue = function(priority, value) {
+  this.insert(priority, value);
+};
+
+
+/**
+ * Retrieves and removes the head of this queue.
+ * @return {*} The element at the head of this queue. Returns
+ *     undefined if the queue is empty.
+ */
+goog.structs.PriorityQueue.prototype.dequeue = function() {
+  return this.remove();
+};