Attempt Number: 3
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
To progress toward the goal state, we need block `b` on block `c`. Since block `c` is already on block `b` and clear, stack(b c) is unnecessary. Instead, let's unstack(c b) so block `c` can be placed on the table.

New State Description:
Block `a` is on block `d` and clear. Block `b` is on the table and clear. Block `c` is held by the hand and not clear. Block `d` is on the table and supporting block `a`. The hand is not empty, holding block `c`.

Action Chosen:
unstack(c b)
