case pred_const_ X xs | pred_var_ X xs | def_ X xs =>
  congr!
  case _ x =>
    constructor
    case mp =>
      tauto
    case mpr =>
      intro a1
      subst a1
      tauto
v t : VarName
X : DefName
xs : List VarName
binders : Finset VarName
h1 : v ∉ binders
⊢ def_ X (List.map (fun x => if v = x ∧ x ∉ binders then t else x) xs) =
    def_ X (List.map (fun x => if v = x then t else x) xs)
no goals