Attempt Number: 2
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
The goal is to place block 'a' on block 'd'. Since block 'a' is currently held in the hand and block 'd' is clear, the best action is to stack 'a' on 'd', moving us closer to the goal state.

New State Description:
Block 'a' is stacked on block 'd', block 'd' is supporting block 'a', and both are on the table. Block 'c' remains on top of block 'b', and block 'b' is supporting block 'c'. The hand is now empty.

Action Chosen:
stack(a, d)
