code: function (a, b) {
          var done = this._done,
              indexOfA,
              comparedWith;
          indexOfA = done.indexOf(a);
          while (-1 < indexOfA) {
              comparedWith = this._getPair(done, indexOfA);
              if (comparedWith === b) {
                  return false; // Already compared
              }
              indexOfA = done.indexOf(a, indexOfA + 1);
          }
          return true;
      }
docs: Check in the stack of done if parameters were never compared
  
  @param {Object} a
  @param {Object} b
  @return {Boolean}