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

Action Reasoning:
The goal is to place block 'a' on block 'c', which is currently clear. The best action is to stack 'a' on 'c' to progress towards the goal state.

New State Description:
The hand is empty. Block 'a' is now on block 'c', making 'a' clear. Block 'c' is no longer clear as it is supporting block 'a'. Block 'b' remains on the table with block 'd' on top of it, and block 'd' is clear.

Action Chosen:
stack(a, c)
