undo_t
undo_t *push_undo_stack(int, long, long);
undo_t *up = NULL;
undo_t *up = NULL;
undo_t *up = NULL;
undo_t *up;
undo_t *ustack = NULL; /* undo stack */
undo_t *
(err = reallocarr(&ustack, usize += USIZE, sizeof(undo_t))) == 0) {
undo_t utmp; \