cmp_relation
if (cmp_relation(rel, &tmp) < 0)
if (cmp_relation(rel, &tmp) == 0)
if (cmp_relation(tmp, &remove) != 0)
if (cmp_relation(one_rel, two_rel) < 0) {
} else if (cmp_relation(one_rel, two_rel) == 0) {