d[rb[0]] = this->(psi, isign, 0); d[rb[1]] = this->(psi, isign, 1);
d[rb[0]] = this->operator()(psi, isign, 0); d[rb[1]] = this->operator()(psi, isign, 1);
  virtual LatticeFermion operator() (const LatticeFermion& psi, int isign) const    {      LatticeFermion d;      d[rb[0]] = this->(psi, isign, 0);      d[rb[1]] = this->(psi, isign, 1);    }