refine nodup_elems.length_le_of_subset ?_
α : Type u
β : Type v
inst✝¹ : BishopFin α
inst✝ : BishopFin β
f : α → β
f_surj : ∀ (b : β), ∃ a, f a = b
⊢ List.length (List.map f (elems α)) ≥ List.length (elems β)
α : Type u
β : Type v
inst✝¹ : BishopFin α
inst✝ : BishopFin β
f : α → β
f_surj : ∀ (b : β), ∃ a, f a = b
⊢ elems β ⊆ List.map f (elems α)