Attempt Number: 3
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, block 'a' should be placed on block 'c', so the best action is to stack 'a' on 'c'.

New State Description:
The hand is empty. Block a is stacked on block c. Block c is on the table and supporting block a. Block b is on the table with block d on top of it. Block d is on block b and is clear.

Action Chosen:
stack(a, c)
