Current State ID: 0
Current State Description: In the initial state, block `b` is on the table. Block `c` is on top of block `b`. Block `a` is on top of block `c`. Block `d` is on top of block `a`. Block `d` is clear, meaning there is no block on top of it. The hand is empty.

Child State ID: 1
Action Taken: unstack(d, a)
State Description: Block `d` is now held by the hand and is no longer clear. Block `a` is clear and on top of block `c`. Block `c` is on top of block `b`. Block `b` is on the table. The hand is holding block `d`.

