title: In AVL-Tree, why needs more one performance of rotation in deletion?
body: <p>let z be the first unbalanced node.</p>
  
  <p>in deletion, after we perform a rotation at z, we may have to perform a rotation at ancestors of z. Thus, we must continue to trace the path until we reach the root.<a href="http://www.geeksforgeeks.org/avl-tree-set-2-deletion/" rel="nofollow noreferrer">http://www.geeksforgeeks.org/avl-tree-set-2-deletion/</a></p>
  
  <p>but why ancestors of z may needs rotation?</p>