tauto
Δ : List Formula
F phi psi : Formula
D : Type
I : Interpretation D
V : VarAssignment D
E : Env
a✝ : ∀ H ∈ [], Holds D I V E H
⊢ ¬(((Holds D I V E phi ↔ Holds D I V E psi) →
        ¬((Holds D I V E phi → Holds D I V E psi) → ¬(Holds D I V E psi → Holds D I V E phi))) →
      ¬(¬((Holds D I V E phi → Holds D I V E psi) → ¬(Holds D I V E psi → Holds D I V E phi)) →
          (Holds D I V E phi ↔ Holds D I V E psi)))
no goals