Attempt Number: 2
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
The block 'a' needs to be on top of block 'c' to reach the goal state. Since 'a' is already held, placing it on 'c' is the best next step.

New State Description:
The hand is empty. Block 'a' is on top of block 'c'. Block 'a' is clear. Block 'b' remains on the table and is clear. Block 'c' is on the table and no longer clear. Block 'd' remains on the table and is clear.

Action Chosen:
stack(a, c)
