simp only [Sub.Var.One.Rec.fastReplaceFree]
D : Type
I : Interpretation D
u v : VarName
a : D
head✝ : Definition
tail✝ : List Definition
tail_ih✝ :
  ∀ (V : VarAssignment D) (F : Formula),
    ¬isFreeIn v F →
      ¬isBoundIn v F →
        (Holds D I (Function.updateITE V u a) tail✝ F ↔
          Holds D I (Function.updateITE V v a) tail✝ (Sub.Var.One.Rec.fastReplaceFree u v F))
X : PredName
xs : List VarName
V : VarAssignment D
h1 : v ∉ xs
h2 : ¬isBoundIn v (pred_var_ X xs)
⊢ Holds D I (Function.updateITE V u a) (head✝ :: tail✝) (pred_var_ X xs) ↔
    Holds D I (Function.updateITE V v a) (head✝ :: tail✝) (Sub.Var.One.Rec.fastReplaceFree u v (pred_var_ X xs))
D : Type
I : Interpretation D
u v : VarName
a : D
head✝ : Definition
tail✝ : List Definition
tail_ih✝ :
  ∀ (V : VarAssignment D) (F : Formula),
    ¬isFreeIn v F →
      ¬isBoundIn v F →
        (Holds D I (Function.updateITE V u a) tail✝ F ↔
          Holds D I (Function.updateITE V v a) tail✝ (Sub.Var.One.Rec.fastReplaceFree u v F))
X : PredName
xs : List VarName
V : VarAssignment D
h1 : v ∉ xs
h2 : ¬isBoundIn v (pred_var_ X xs)
⊢ Holds D I (Function.updateITE V u a) (head✝ :: tail✝) (pred_var_ X xs) ↔
    Holds D I (Function.updateITE V v a) (head✝ :: tail✝) (pred_var_ X (List.map (fun x => if u = x then v else x) xs))