Current State ID: 0
Current State Description: In the initial state, we have four blocks: a, b, c, and d. Block a is on the table with block d on top of it, and block d is clear. Block b is on the table with block c on top of it, and block c is clear. The hand is empty.

Child State ID: 1
Action Taken: unstack(d a)
State Description: Block `a` is on the table and clear. Block `d` is held by the hand and is no longer clear. Block `b` is on the table supporting block `c`, which is clear. The hand is holding block `d`.

