OLattice<T>& d = dd.field(); const S& s = dd.subset();  zero_rep(d,s);
void zero_rep(OLattice<T>& dest, const UnorderedSubset& s) {#if ! defined(QDP_NOT_IMPLEMENTED)  const int *tab = s.siteTable().slice();  for(int j=0; j < s.numSiteTable(); ++j)   {    int i = tab[j];    zero_rep(dest.elem(i));  }#else  QDP_error("zero_rep_UnorderedSubset not implemented");#endif}