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 'c' must be on the table. Since it is currently on top of block 'd', we need to unstack 'c' from 'd'.

New State Description:
The hand is holding block 'c'. Block 'b' is on the table and clear. Block 'a' is on the table. Block 'd' is on top of block 'a' and is clear. Block 'c' is no longer on block 'd'.

Action Chosen:
unstack(c, d)
