∀ {α : Type u} [inst : BEq α] [inst_1 : Hashable α] {β : Type v} [EquivBEq α] [LawfulHashable α]
  (m : Std.DHashMap.Internal.Raw₀ α fun x => β),
  (↑m).WF →
    ∀ {k : α} {f : Option β → Option β},
      (↑(Std.DHashMap.Internal.Raw₀.Const.alter m k f)).isEmpty =
        ((↑(m.erase k)).isEmpty && (f (Std.DHashMap.Internal.Raw₀.Const.get? m k)).isNone)