simp
case h.e'_2
v t : VarName
X : DefName
xs : List VarName
h1 : t ∉ xs
⊢ ∀ x ∈ xs, ((fun x => if t = x then v else x) ∘ fun x => if v = x then t else x) x = x
case h.e'_2
v t : VarName
X : DefName
xs : List VarName
h1 : t ∉ xs
⊢ ∀ x ∈ xs, (if t = if v = x then t else x then v else if v = x then t else x) = x