code: function (fact, cb) {
              //fact = this.workingMemory.getFact(fact);
              this.retract(fact);
              if ("function" === typeof cb) {
                  cb.call(fact, fact);
              }
              this.emit("modify", fact);
              return this.assert(fact);
          }
docs: This method is called to alter an existing fact.  It is essentially a retract followed by an assert.