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

Action Reasoning:
To achieve the goal state, block 'b' should be placed on block 'c'. Since the hand is currently holding block 'b' and block 'c' is clear and on the table, the best action is to stack 'b' on 'c'.

New State Description:
Block 'b' is now on top of block 'c', and block 'c' is supporting block 'b'. The hand is empty. Block 'a' remains on top of block 'd', with block 'd' supporting block 'a'. Both block 'a' and block 'b' are clear.

Action Chosen:
stack(b, c)
