∀ {α : Type u} {β : α → Type v} [inst : BEq α] [EquivBEq α] {f : α → Bool} {l : List ((a : α) × β a)} {k : α},
  Std.Internal.List.DistinctKeys l →
    Std.Internal.List.getKey? k (List.filter (fun p => f p.fst) l) = Option.filter f (Std.Internal.List.getKey? k l)