case _ =>
  rfl
D : Type
I : Interpretation D
u v : VarName
a : D
hd : Definition
tl : List Definition
ih :
  ∀ (V : VarAssignment D) (F : Formula),
    ¬isFreeIn v F →
      ¬isBoundIn v F →
        (Holds D I (Function.updateITE V u a) tl F ↔
          Holds D I (Function.updateITE V v a) tl (Sub.Var.One.Rec.fastReplaceFree u v F))
X : DefName
xs : List VarName
V : VarAssignment D
h1 : v ∉ xs
h2 : ¬isBoundIn v (def_ X xs)
c1 : X = hd.name ∧ (List.map (fun x => if u = x then v else x) xs).length = hd.args.length
v' : VarName
a1 : isFreeIn v' hd.q
x : VarName
a2 : x ∈ xs
h✝¹ : ¬u = x
h✝ : ¬v = x
⊢ V x = V x
no goals