simp only [IsValid] at h2
F : Formula
P : PredName
zs : List VarName
H : Formula
h1 : admits P zs H F
h2 : F.IsValid
⊢ (replace P zs H F).IsValid
F : Formula
P : PredName
zs : List VarName
H : Formula
h1 : admits P zs H F
h2 : ∀ (D : Type) (I : Interpretation D) (V : VarAssignment D) (E : Env), Holds D I V E F
⊢ (replace P zs H F).IsValid