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

Action Reasoning:
To move closer to the goal state, we should stack block 'a' on block 'c', which will set the stage for placing block 'd' on 'a' in the next steps.

New State Description:
The hand is empty. Block 'a' is on top of block 'c', so block 'c' is not clear. Block 'a' is clear because nothing is on it. Block 'b' is on the table and clear. Block 'd' is on the table and clear.

Action Chosen:
stack(a, c)
