Algo(T, k)
    Stack S = Ø
    curr = T
    prev = next = NIL

    while (S ≠ Ø OR curr ≠ NIL) AND next ≠ NIL do
        if curr ≠ NIL then
            push(S, curr)
            curr = curr->sx
        else
            curr = pop(S)
            if curr->key < k then
                prev = curr
            if curr->key > k then
                next = curr
            curr = curr->dx