Attempt Number: 4
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 separate the blocks. The only clear block on top of the stack is block d, so we'll start by unstacking it from block a.

New State Description:
Block d is in the hand and no longer on block a. Block a is clear. Blocks b and c remain in their original positions. The hand is holding block d, and block d is not clear.

Action Chosen:
unstack(d, a)
