struct tavl_node *x = y->tavl_link[1];

assert (x != NULL);
if (x->tavl_balance == -1)
  {
    struct tavl_node *w;

    assert (x->tavl_balance == -1);
    w = x->tavl_link[0];
    x->tavl_link[0] = w->tavl_link[1];
    w->tavl_link[1] = x;
    y->tavl_link[1] = w->tavl_link[0];
    w->tavl_link[0] = y;
    if (w->tavl_balance == +1)
      x->tavl_balance = 0, y->tavl_balance = -1;
    else if (w->tavl_balance == 0)
      x->tavl_balance = y->tavl_balance = 0;
    else /* |w->tavl_balance == -1| */
      x->tavl_balance = +1, y->tavl_balance = 0;
    w->tavl_balance = 0;
    if (w->tavl_tag[0] == TAVL_THREAD)
      {
        y->tavl_tag[1] = TAVL_THREAD;
        y->tavl_link[1] = w;
        w->tavl_tag[0] = TAVL_CHILD;
      }
    if (w->tavl_tag[1] == TAVL_THREAD)
      {
        x->tavl_tag[0] = TAVL_THREAD;
        x->tavl_link[0] = w;
        w->tavl_tag[1] = TAVL_CHILD;
      }
    q->tavl_link[dir] = w;
  }
else
  {
    q->tavl_link[dir] = x;

    if (x->tavl_balance == 0)
      {
        y->tavl_link[1] = x->tavl_link[0];
        x->tavl_link[0] = y;
        x->tavl_balance = -1;
        y->tavl_balance = +1;
        break;
      }
    else /* |x->tavl_balance == +1| */
      {
        if (x->tavl_tag[0] == TAVL_CHILD)
          y->tavl_link[1] = x->tavl_link[0];
        else
          {
            y->tavl_tag[1] = TAVL_THREAD;
            x->tavl_tag[0] = TAVL_CHILD;
          }
        x->tavl_link[0] = y;
        y->tavl_balance = x->tavl_balance = 0;
      }
  }
