Attempt Number: 3
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, we need to move block 'c' to the table to clear block 'b'. This will allow us to stack 'a' on 'b' later.

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

Action Chosen:
unstack(c, b)
