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

Action Reasoning:
The goal is to stack block 'a' on block 'c'. Since 'a' is currently being held and 'c' is clear and on the table, we can stack 'a' on 'c' to align with the goal state.

New State Description:
Block 'a' is now on top of block 'c'. Block 'a' is not clear, and it is no longer being held. The hand is empty. Block 'c' remains on the table and is no longer clear. Block 'b' is on the table with block 'd' on top of it, and block 'd' is clear.

Action Chosen:
stack(a, c)
