simp
case nil
α : Type u_1
inst✝ : BEq α
h : ([] == []) = true
⊢ [] = []

case cons
α : Type u_1
inst✝ : BEq α
head✝ : α
tail✝ : List α
h : (head✝ :: tail✝ == []) = true
⊢ head✝ :: tail✝ = []
case cons
α : Type u_1
inst✝ : BEq α
head✝ : α
tail✝ : List α
h : (head✝ :: tail✝ == []) = true
⊢ head✝ :: tail✝ = []