∀ {γ : Type u} {α β : Type v} [inst : Std.ToIterator (Std.Slice γ) Id α β] [inst_1 : Std.Iterator α Id β]
  {s : Std.Slice γ} [inst_2 : Std.Slice.SliceSize γ] [Std.Slice.LawfulSliceSize γ] [Std.Iterators.Finite α Id],
  s.size = s.toList.length