Attempt Number: 4
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
The next best action is to stack block 'a' on block 'd' because it directly moves block 'a' towards its goal state position, where 'a' is on top of 'd'.

New State Description:
Block 'a' is now on top of block 'd', making block 'a' clear and no longer held. Block 'd' is no longer clear as it supports block 'a'. Block 'b' is still on the table with block 'c' on top of it. The hand is now empty.

Action Chosen:
stack(a, d)
