;; stack operations
(new-stack)
(stack-pop! stk)
(stack-push! stk elem)
(stack-top stk)
(stack-remove! stk key)
(stack-empty? stk)

;; queue operations
(new-queue)
(queue-out! q)
(queue-in! q elem)
(queue-head q)
(queue-tail q)
(queue-remove! q key)
(queue-empty? q)