make sure delete gc[n] is safe

                        nxlo_out[n],nxhi_out[n],nylo_out[n],nyhi_out[n],nzlo_out[n],nzhi_out[n],

                        procneigh[0][0],procneigh[0][1],procneigh[1][0],

                        procneigh[1][1],procneigh[2][0],procneigh[2][1]);

    }

    } else cg[n] = nullptr;

  }

}