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

Action Reasoning:
To progress towards the goal state, we should stack block 'a' on block 'c', as block 'c' is clear and 'a' is currently being held.

New State Description:
The hand is now empty. Block 'a' is on block 'c'. Block 'c' is supporting block 'a' and is not clear. Block 'b' is supporting block 'd' and is not clear. Block 'd' is on block 'b' and is clear.

Action Chosen:
stack(a, c)
