intros x xs
α : Type u_1
inst✝ : DecidableEq α
⊢ ∀ (x : α) (xs : List α), removeAll (x :: xs) [x] = removeAll xs [x]
α : Type u_1
inst✝ : DecidableEq α
x : α
xs : List α
⊢ removeAll (x :: xs) [x] = removeAll xs [x]