∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : Type v} {m : Std.ExtDHashMap α fun x => β} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] {f : α → β → Bool} {k : α},
  (Std.ExtDHashMap.filter f m).getKey? k = (m.getKey? k).pfilter fun x_2 h' => f x_2 (Std.ExtDHashMap.Const.get m x_2 ⋯)