code: public static <E> SortedSet<E> constrainedSortedSet(
        SortedSet<E> sortedSet, Constraint<? super E> constraint) {
      return new ConstrainedSortedSet<E>(sortedSet, constraint);
    }
docs: Returns a constrained view of the specified sorted set, using the specified
  constraint. Any operations that add new elements to the sorted set will
  call the provided constraint. However, this method does not verify that
  existing elements satisfy the constraint.
  
  <p>The returned set is not serializable.
  
  @param sortedSet the sorted set to constrain
  @param constraint the constraint that validates added elements
  @return a constrained view of the sorted set