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

Action Reasoning:
To achieve the goal state, we need to move block 'b' onto block 'a'. Since block 'a' is clear, we can unstack block 'd' from block 'b' to free block 'b' for stacking.

New State Description:
The hand is holding block 'd'. Block 'b' is clear and on the table. Block 'a' is on block 'c' and is clear. Block 'c' is supporting block 'a' and is no longer clear. Block 'd' is no longer on block 'b'.

Action Chosen:
unstack(d, b)
