∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : α → Type v} {m : Std.ExtDHashMap α β} [inst : LawfulBEq α]
  {f : (a : α) → β a → Bool} {k : α} [inst_1 : Inhabited (β k)],
  (Std.ExtDHashMap.filter f m).get! k = (Option.filter (f k) (m.get? k)).get!