apply ListN.heq
case mk
α : Type u_1
n : Nat
toList✝ : List α
length_eq✝ : toList✝.length = n
⊢ { toList := toList✝, length_eq := length_eq✝ }.append nil ≅ { toList := toList✝, length_eq := length_eq✝ }
case mk.a
α : Type u_1
n : Nat
toList✝ : List α
length_eq✝ : toList✝.length = n
⊢ α = α

case mk.a
α : Type u_1
n : Nat
toList✝ : List α
length_eq✝ : toList✝.length = n
⊢ 0 + n = n

case mk.a
α : Type u_1
n : Nat
toList✝ : List α
length_eq✝ : toList✝.length = n
⊢ ({ toList := toList✝, length_eq := length_eq✝ }.append nil).toList ≅
    { toList := toList✝, length_eq := length_eq✝ }.toList