Current State ID: 20
Current State Description: Block 'a' is held in the hand and no longer on the table. Blocks 'b', 'c', and 'd' remain clear and on the table. The hand is no longer empty.

Child State ID: 29
Action Taken: stack(a, 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.

