**Statement:** [[075_D9.1_Grace-Operator-Definition|Grace operator]] Ĝ is non-unitary (information added, not just transformed).
Theorem: Any operator that maps multiple states to a single state is non-unitary.
Proof:
1. Ĝ|-1⟩ = |+1⟩ and Ĝ|+1⟩ = |+1⟩
2. Both |-1⟩ and |+1⟩ map to the same output
3. Unitary operators are bijective (one-to-one)
4. Ĝ is not bijective (two inputs → one output)
5. Therefore, Ĝ is not unitary
Corollary: Grace cannot be reversed. There's no Ĝ⁻¹ that uniquely recovers the pre-grace state.