{α : Type u} →
  {motive : Std.DTreeMap.Internal.Unit.RiiSliceData α → Sort u_1} →
    ((treeMap : Std.DTreeMap.Internal.Impl α fun x => Unit) →
        (range : Std.Rii α) → motive { treeMap := treeMap, range := range }) →
      (t : Std.DTreeMap.Internal.Unit.RiiSliceData α) → motive t