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

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

