/**
   * Determines whether all elements of an observable sequence satisfy a condition.
   * @param {Function} [predicate] A function to test each element for a condition.
   * @param {Any} [thisArg] Object to use as this when executing callback.
   * @returns {Observable} An observable sequence containing a single element determining whether all elements in the source sequence pass the test in the specified predicate.
   */
  observableProto.every = function (predicate, thisArg) {
    return this.filter(function (v) { return !predicate(v); }, thisArg).some().map(not);
  };

  /** @deprecated use #every instead */
  observableProto.all = function () {
    //deprecate('all', 'every');
    return this.every.apply(this, arguments);
  };