Parent State ID: 6
State Depth: 5
Action Taken: unstack(c, b)
Action Reasoning: To reach the goal state, block `d` needs to be on top of block `b`. The next logical step is to move block `c` from block `b` to clear the path for stacking block `d` on block `b`.
State Description: Block `a` is on top of block `d` and is clear. Block `d` is on the table and supports block `a`. Block `c` is now held by the hand, making block `b` clear and on the table. The hand is holding block `c`.
Action Path: ['unstack(d, a)', 'put-down(d)', 'unstack(a, c)', 'stack(a, d)', 'unstack(c, b)']

INACTIVE REASON: action path invalid: The last action `unstack(c, b)` is invalid because the precondition that the hand must be empty is not met. The hand was holding `a` after the previous action `stack(a, d)`. Therefore, the current state's description and visualization are based on an invalid action.
