NF_ACYCLIC
if (!(n->n_flags & NF_ACYCLIC)) {
n->n_flags |= NF_ACYCLIC;
if (from->n_flags & (NF_NODEST|NF_MARK|NF_ACYCLIC))
if ((*np)->n_flags & (NF_MARK|NF_ACYCLIC|NF_NODEST))