Parent State ID: 20
State Depth: 6
Action Taken: stack(a, d)
Action Reasoning: The goal is to place block 'a' on top of block 'd'. Since 'a' is currently held and 'd' is clear and on the table, the best action is to stack 'a' on 'd'.
State Description: Block 'a' is now on top of block 'd', and both blocks 'b' and 'c' remain clear and on the table. The hand is empty. In the diagram, 'a' is stacked on 'd', and the hand is no longer holding any block.
Action Path: ['unstack(d, a)', 'put-down(d)', 'unstack(c, b)', 'put-down(c)', 'pick-up(a)', 'stack(a, d)']
