Current State ID: 41
Current State Description: The hand is now empty. Block 'a' is on block 'c', and block 'c' is no longer clear. Block 'b' is on the table with block 'd' on top of it, and block 'd' is clear. The diagram now shows block 'a' on block 'c'.

Child State ID: 50
Action Taken: unstack(d, b)
State Description: The hand is holding block 'd'. Block 'b' is now clear and on the table. Block 'a' is on block 'c', and block 'c' is on the table. The diagram will show block 'd' being held by the hand, with block 'b' clear and on the table.

Child State ID: 51
Action Taken: pick-up(b)
State Description: The hand is now holding block 'b'. Block 'a' remains on block 'c', and block 'd' is on the table and clear. Block 'b' is no longer on the table.

