Current State ID: 6
Current State Description: Block `a` is now on top of block `d` and is clear. Block `d` is on the table but is no longer clear because block `a` is on it. Block `c` remains clear and on top of block `b`. Block `b` is on the table. The hand is empty.

Child State ID: 9
Action Taken: unstack(c, b)
State Description: Block `c` is now held in the hand and is no longer on block `b`. Block `b` is on the table and is clear. Block `a` is on block `d` and is clear. Block `d` remains on the table but is supporting block `a`. The hand is holding block `c`.

