Attempt Number: 2
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 'a' on 'd' because it directly moves us closer to the goal state where 'a' is on top of 'd', and the hand is already holding 'a'.

New State Description:
Block 'a' is now on top of block 'd', making block 'd' not clear. Block 'a' is clear. The hand is empty. Block 'b' remains on the table with block 'c' on top of it, unchanged.

Action Chosen:
stack(a, d)
