code: public SameDiff dup() {
          Cloner cloner = newCloner();
          SameDiff clone = cloner.deepClone(this);
          //TODO don't clone sessions in the first place!
          clone.sessions.clear();
          return clone;
      }
docs: Clone/duplicate the SameDiff instance, including arrays etc. The returned SameDiff instance should have no
  shared state with the original instance
  @return The cloned SameDiff instance