code: function (leftContext, rightContext) {
              var leftMatch = leftContext.match,
                  fh = leftMatch.factHash,
                  alias = this.__alias,
                  rightFact = rightContext.fact;
              fh[alias] = rightFact.object;
              var ret = this.constraint.assert(fh);
              fh[alias] = null;
              return ret;
  
          }
docs: used by NotNode to avoid creating match Result for efficiency