(function($) {

"use strict";

try {

    Object.defineProperties($.prototype, {

        hasEquivalence: {
            value: function(key) {
                var
                    iterator = this.keys(),
                    tuple = iterator.next();

                while (!tuple.done) {
                    if (Object.areEquivalents(tuple.value, key)) {
                        return true;
                    }

                    tuple = iterator.next();
                }

                return false;
            }
        }

    });
} catch(e) {}

})(Map);