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

Action Reasoning:
Currently, block `a` is held by the hand, which is necessary to achieve the next desired configuration. The best action now is to stack block `a` on top of block `d`, which is clear, as this directly contributes to reaching the final goal state.

New State Description:
Block `a` is on block `d` and clear. Block `b` is on the table and not clear, as it supports block `d`. Block `c` is on the table and clear. Block `d` is on block `b` and not clear, but it supports block `a`. The hand is empty.

Action Chosen:
stack(a, d)
