code: function(_set1, _set2) {
          var flagEquals,
              newSet = [];
          for (var i = 0; i < _set1.length; i++) {
              flagEquals = false;
              for(var j = 0; j < _set2.length; j++) {
                  if (_set1[i].asString == _set2[j].asString) {
                      flagEquals = true;
                      break;
                  }
              }
              if (!flagEquals) {
                  newSet.push(_set1[i]);
              }
          }
  
          return newSet;
      }
docs: Substracts each set.
  Not to be used in tag-based reasoning.
  @param _set1
  @param _set2
  @returns {Array}