w = x->tavl_link[1];
rotate_left (&y->tavl_link[0]);
rotate_right (&z->tavl_link[y != z->tavl_link[0]]);
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;
