"In my Data Structures course in college, when we got to AVL trees, my prof turned and wrote on the board, in huge, clear letters:

AVL Trees are EVIL

...and that's all we had to learn about them. He had us implement red/black trees and splay trees instead. To this day, I have no idea how threaded AVL trees work. But if that's OK with Dan Weld, it's OK with me. "

Thank goodness it wasn't: "LISP is EVIL". Or replace lisp by anything useful and generally misunderstood.