∀ {α : Type u} [inst : BEq α] [EquivBEq α] {β : Type v} {γ : Type w} {f : α → β → Option γ} {l : List ((_ : α) × β)}
  {k : α},
  Std.Internal.List.DistinctKeys l →
    Std.Internal.List.containsKey k (List.filterMap (fun p => Option.map (fun x => ⟨p.fst, x⟩) (f p.fst p.snd)) l) =
      if h : Std.Internal.List.containsKey k l = true then
        (f (Std.Internal.List.getKey k l h) (Std.Internal.List.getValue k l h)).isSome
      else false