Attempt Number: 4
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
The goal is to place block 'd' on the table and block 'a' on top of it. By unstacking block 'd' from block 'a', 'd' will be in hand and can be put on the table.

New State Description:
Block d is now held in the hand. Block a is clear and on the table. Block b is on top of block c, with both on the table. The hand is not empty.

Action Chosen:
unstack(d, a)
