∀ {α : Type u_1} {β : Type u_2} {xs : Array α} {ys zs : Array β} {f : α → Option β},
  (Array.filterMap f xs = ys ++ zs) = ∃ as bs, xs = as ++ bs ∧ Array.filterMap f as = ys ∧ Array.filterMap f bs = zs