∀ {α : Type u} {β : α → Type v} [inst : Ord α] [Std.TransOrd α] (t : Std.DTreeMap.Internal.Impl α β),
  t.Ordered →
    ∀ (z : Std.DTreeMap.Internal.Zipper α β) (lowerBound : α),
      Std.DTreeMap.Internal.Zipper.prependMap (Std.DTreeMap.Internal.Impl.pruneLT✝ t lowerBound) z =
        Std.DTreeMap.Internal.Zipper.prependMapGT t lowerBound z