Axioms for RA-Stacks

• Pushing an item onto a stack should result in the item being on the top:

       (top-minus (push! ra-stack item) 0) = item     

• If an item is k elements from the top of a stack, then after the stack is pushed it is k+1 elements from the top:

       (top-minus ra-stack k) = (top-minus (push! ra-stack item) (+ k 1))
       

• If an item is k elements from the top of a stack, then after the stack is popped it is k-1 elements from the top:

       (top-minus ra-stack k) = (top-minus (pop! ra-stack) (- k 1))     

Other axioms state how other ra-stack ADT procedures are related (Exercise 13.6).

These axioms can guide the underlying ra-stack implementation.