undo_t
undo_t *push_undo_stack(int, int, int);
undo_t *up = NULL;
undo_t *up = NULL;
undo_t *up = NULL;
undo_t *up;
static undo_t *ustack = NULL; /* undo stack */
undo_t *
undo_t *t;
(t = reallocarray(ustack, (usize += USIZE), sizeof(undo_t))) != NULL) {
undo_t utmp; \