Backward Chaining

• You can only simulate a backward chained plan.
• You start at the goal state, and consider the moves that can take you there.
• Using the same example, the initial state is: On(B, Ground), On(A, Ground), On(C,A), Clear(B) and Clear(C).
• The goal state is: On(C, Ground), On(B, C), and On(A,B).
• The only move you can make to get here is Move(A,B,Ground).
• However, from this state, you can choose Move(A,Ground,B), Move(B,C,Ground), or Move(B,A,C).
• You can ignore the one that takes you back to the goal state.
• In reverse, what you want to do is:
• you want to, as the last step Move(A,Ground,B), before that, Move(B,Ground,C) and intially Move(C,A,Ground).
• What is a good algorithm to explore this space?
• Depth first search isn't good because you have infinite chains; you can fix this by making sure not to revisit states.
• What about clear?
• We've just mentioned the moves, not the ongoing description of the states.