Parent State ID: 20
State Depth: 8
Action Taken: stack(a, b)
Action Reasoning: To achieve the goal state, we need to place block 'a' on block 'b'. Since the hand is currently holding block 'a' and block 'b' is clear, the best action is to stack 'a' on 'b'.
State Description: Block 'a' is on top of block 'b' and is clear. Block 'b' is on the table and supporting block 'a'. Block 'c' is on top of block 'b' and is supporting block 'd'. Block 'd' is on top of block 'c' and is clear. The hand is empty.
Action Path: ['unstack(d, a)', 'put-down(d)', 'unstack(a, c)', 'put-down(a)', 'pick-up(d)', 'stack(d, c)', 'pick-up(a)', 'stack(a, b)']

INACTIVE REASON: deactivated because diagram generation failed or invalid action chosen: Block 'b' is not clear, violating the precondition for stacking.
