Problem: Pointers to stacks need mailboxes

Norman doesn’t have any trays.  He has to use pieces of paper and mailboxes and has to remember where the top of the stack is at any moment. 
If he remembers that the top of the stack is 212, then he can pop a byte by taking the piece of paper out of mailbox 212, but then he has to remember that the top of the stack is now 211.