inorder_next
BUG_ON(inorder_prev(inorder_next(j, size), size) != j);
j = inorder_next(j, size);
for (j = inorder_next(0, t->size);
j = inorder_next(j, t->size)) {
for (j = inorder_next(0, t->size);
j = inorder_next(j, t->size))
f = &t->tree[inorder_next(j, t->size)];