Current State ID: 0
Current State Description: There are four blocks: a, b, c, and d. The hand is empty. Block b is on the table, and block c is on the table. Block a is on top of block b, and block d is on top of block c. Both blocks a and d are clear, meaning there are no blocks on top of them.

Child State ID: 1
Action Taken: unstack(d, c)
State Description: Block a is on block b, block c is on the table, and block d is held in the hand. Blocks a and c are clear. The hand is not empty.

