simp
v t : VarName
X : DefName
xs : List VarName
binders : Finset VarName
h1 : t ∉ xs
⊢ t ∈ List.map (fun x => if v = x ∧ x ∉ binders then t else x) xs → v ∉ binders
v t : VarName
X : DefName
xs : List VarName
binders : Finset VarName
h1 : t ∉ xs
⊢ ∀ x ∈ xs, ((v = x → x ∈ binders) → x = t) → v ∉ binders