simp only [Holds]
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.and_ psi).iff_ (phi.imp_ psi.not_).not_)
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)