Deletion

Given a value X and an AVL tree T, delete the node containing X and rebalance the result.

Deleting X upsets A.

After rotating B up, E is upset.

After rotating F up, D's left subtree is shorter. D is upset.

After rotating M up (D down), we get a 5-5 balance at D. So now it is 1 shorter and its parent is out of balance.

This can propagate all the way to the top of the tree.