/* An instance of an implementing class is for the purpose of distinguishing
** between two categories of values among elements of whatever type is
** used in instantiating the generic type parameter T.  The two categories 
** are referred to as RED and BLUE, just for fun.
** 
** Note: Conceivably, an implementing class could be used for distinguishing
** among four categories: RED, BLUE, both, or neither.
*/
public interface RedBlueClassifier<T> {

   /* Returns true iff the given element is in the RED category.
   */
   boolean isRed(T elem);

   /* Returns true iff the given element is in the BLUE category.
   */
   boolean isBlue(T elem);
}