l_difference
l_difference(ilm->ilm_filter, flist, a_minus_b);
l_difference(flist, ilm->ilm_filter, b_minus_a);
l_difference(ilm->ilm_filter, flist, a_minus_b);
l_difference(flist, ilm->ilm_filter, b_minus_a);
l_difference(ilm->ilm_pendsrcs,
l_difference(ilm->ilm_pendsrcs,
l_difference(&fbld.fbld_ex, &fbld.fbld_in, flist);
void l_difference(const slist_t *, const slist_t *, slist_t *);