Current State ID: 7
Current State Description: Block `a` is on block `d` and clear. Block `b` is on the table supporting block `c`, which is clear. Block `c` is on block `b` and clear. Block `d` is on the table and supporting block `a`. The hand is empty.

Child State ID: 9
Action Taken: unstack(c b)
State Description: Block `a` is on block `d` and clear. Block `b` is on the table and clear. Block `c` is in the hand and not clear. Block `d` is on the table and supporting block `a`. The hand is holding block `c`.

