∀ {α : Type u} {β : α → Type v} [inst : Ord α] (k : α) (v : β k) (t : Std.DTreeMap.Internal.Impl α β) (hl : t.Balanced),
  Std.DTreeMap.Internal.Impl.containsThenInsertIfNew k v t hl =
    if Std.DTreeMap.Internal.Impl.contains k t = true then
      (true, { impl := t, balanced_impl := ⋯, lb_le_size_impl := ⋯, size_impl_le_ub := ⋯ })
    else (false, Std.DTreeMap.Internal.Impl.insert k v t ⋯)