The Towers of Hanoi

• One really well known problem is the towers of Hanoi.
• There are three pegs (123), and several differently sized discs (e.g. ABCD).
• You can only move one disc at a time, and a bigger disc can never sit on a smaller one.
• Initially, ABCD are on peg one. The goal is to move them to another.
• How do you break that down to subgoals?
• How do you fulfill the subgoals?
• At this point, you need a goal stack.
• That is you build the subgoals until you can resolve one with an atomic action.
• You then manage the stack.
• The tower of Hanoi is also used to describe recursion.
• However, stack management doesn't always work.
• One of the problems is protecting your already fulfilled goals.