Attempt Number: 2
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
The hand is currently holding block `b`. To reach the goal state, block `b` should be placed on top of block `c`, which is currently clear on the table. The next best action is to stack block `b` onto block `c`.

New State Description:
Block `a` is on block `d` and clear. Block `b` is on block `c` and clear. Block `c` is on the table and supporting block `b`. Block `d` is on the table and supporting block `a`. The hand is empty.

Action Chosen:
stack(b c)
