α : Type u_1
a : α
as bs : List α
h : bs = a :: as
⊢ (?head :: as).length = bs.length

case head
α : Type u_1
a : α
as bs : List α
h : bs = a :: as
⊢ α
α : Type u_1
b a : α
as bs : List α
h : as = bs
⊢ as.length + 1 + 1 = bs.length + 2
α : Type u_1
b a : α
as bs : List α
h : as = bs
⊢ as.length + 1 + 1 = (b :: bs).length + 1
α : Type u_1
b a : α
as bs : List α
h : as = bs
⊢ as.length + 1 + 1 = bs.length + 1 + 1
α : Type u_1
b a : α
as bs : List α
h : as = bs
⊢ id (a :: b :: as).length = (b :: bs).length + 1
α : Type u_1
b a : α
as bs : List α
h : as = bs
⊢ (a :: b :: as).length = (b :: bs).length + 1
α : Type u_1
b a : α
as bs : List α
h : as = bs
⊢ as.length + 1 + 1 = bs.length + 1 + 1