avl-tree-stack-first is a compiled Lisp function in `avl-tree.el'.

(avl-tree-stack-first AVL-TREE-STACK &optional NILFLAG)

Return the first element of AVL-TREE-STACK, without removing it
from the stack.

Returns nil if the stack is empty, or NILFLAG if specified.
(The latter allows an empty stack to be distinguished from
a null element stored in the AVL tree.)