∀ {α : Type u} [inst : BEq α] [inst_1 : EquivBEq α] {β : Type v} {l : List ((_ : α) × β)} {f : α → β → Bool},
  Std.Internal.List.DistinctKeys l →
    Std.Internal.List.keys (List.filter (fun x => f x.fst x.snd) l) =
      (List.filter (fun x => f (↑x) (Std.Internal.List.getValue (↑x) l ⋯)) (Std.Internal.List.keys l).attach).unattach