Parent State ID: 18
State Depth: 7
Action Taken: stack(a, b)
Action Reasoning: To achieve the goal state, we need 'a' on top of 'b'. Since 'a' is clear and on the table, we can stack 'a' on 'b' directly.
State Description: Block 'a' is on top of block 'b' and clear. Block 'c' is clear and on top of block 'b'. Block 'b' is on the table and supporting 'a'. Block 'd' is on the table and clear. The hand is empty.
Action Path: ['unstack(d, a)', 'put-down(d)', 'unstack(a, c)', 'put-down(a)', 'pick-up(d)', 'put-down(d)', 'stack(a, b)']

INACTIVE REASON: deactivated because diagram generation failed or invalid action chosen: Preconditions for stack(a, b) are not satisfied; b is not clear and the hand is not holding a.
