rw [cons_append]
α✝ : Type u₁
β : Type u₂
γ✝ : α✝ → β → Type v
α : Type u
γ : α → α → Type v
f : (a : α) → γ a a
head✝ : α
as bs : List α
⊢ cons (f head✝) (fromList γ f (as ++ bs)) = cons (f head✝) (fromList γ f as) ++ fromList γ f bs
α✝ : Type u₁
β : Type u₂
γ✝ : α✝ → β → Type v
α : Type u
γ : α → α → Type v
f : (a : α) → γ a a
head✝ : α
as bs : List α
⊢ cons (f head✝) (fromList γ f (as ++ bs)) = cons (f head✝) (fromList γ f as ++ fromList γ f bs)