code: function(fact) {
          if ((this.explicit != fact.explicit) ||
              (this.subject != fact.subject) ||
              (this.predicate != fact.predicate) ||
              (this.object != fact.object)) {
              return false;
          }
          return true;
      }
docs: Checks if the fact is equivalent to another fact.
  @param fact
  @returns {boolean}