simp only [List.map_eq_map_iff]
case h.e'_2
X : DefName
xs : List VarName
σ σ' : VarName → VarName
h1 : ∀ v ∈ xs, σ v = σ' v
⊢ List.map σ xs = List.map σ' xs
case h.e'_2
X : DefName
xs : List VarName
σ σ' : VarName → VarName
h1 : ∀ v ∈ xs, σ v = σ' v
⊢ ∀ x ∈ xs, σ x = σ' x