check_propnames
check_propnames(t, np->u.expr.left, from, to);
check_propnames(t, np->u.expr.right, from, to);
check_propnames(t, np->u.arrow.lhs, 1, to);
check_propnames(t, np->u.arrow.rhs, from, 1);
void check_propnames(enum nodetype t, struct node *np, int from, int to);
check_propnames(t, np, 0, 0);
check_propnames(t, np, 0, 0);