subst h1_2
V P_U P_V : Formula
l : List VarName
h1_P h1_P' : Formula
h1_2 : h1_P' = V
h2 : ∀ (v : VarName), (isFreeIn v h1_P ∨ isFreeIn v V) ∧ isBoundIn v h1_P → v ∈ l
⊢ IsProof ((Forall_ l (h1_P.iff_ V)).imp_ (h1_P.iff_ h1_P'))
P_U P_V : Formula
l : List VarName
h1_P h1_P' : Formula
h2 : ∀ (v : VarName), (isFreeIn v h1_P ∨ isFreeIn v h1_P') ∧ isBoundIn v h1_P → v ∈ l
⊢ IsProof ((Forall_ l (h1_P.iff_ h1_P')).imp_ (h1_P.iff_ h1_P'))