case none => exact h_ind hchain.tail
α : Type u
r : α → α → Prop
inst✝ : Trans r r r
β : Type v
r' : β → β → Prop
f : α → Option β
rel_pres : ∀ (a₁ a₂ : α), r a₁ a₂ → ∀ (b₁ b₂ : β), f a₁ = some b₁ → f a₂ = some b₂ → r' b₁ b₂
a : α
as : List α
h_ind : Ascending r as → Ascending r' (filterMap f as)
hchain : Ascending r (a :: as)
hfa : f a = none
⊢ Ascending r' (filterMap f as)
no goals