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.not_.imp_ psi.not_).imp_ (psi.imp_ phi))
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 psi → Holds D I V E phi