itree_next_constraint
if (itree_next_constraint(ap->arrowp, NULL))
for (cp = itree_next_constraint(ap->arrowp, NULL); cp;
cp = itree_next_constraint(ap->arrowp, cp)) {
if (itree_next_constraint(ap->arrowp, cp))
if (itree_next_constraint(ap->arrowp, NULL))
struct constraintlist *itree_next_constraint(struct arrow *arrowp,