Attempt Number: 4
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
Block `d` is clear and already on the table. Next, we should unstack block `a` from block `c` to place it on top of block `d` later, moving closer to the goal.

New State Description:
Block `a` is now in the hand and no longer clear, previously on top of block `c`. Block `c` is on top of block `b` and is now clear. Block `b` remains on the table supporting block `c`. Block `d` is clear and on the table. The hand is holding block `a` and is not empty.

Action Chosen:
unstack(a, c)
