public interface Comparator {

   public boolean isLess(Object a, Object b) throws InvalidElementException;
   public boolean isLessOrEqual(Object a, Object b) throws InvalidElementException;
   public boolean areEqual(Object a, Object b) throws InvalidElementException;
   public boolean isGreater(Object a, Object b) throws InvalidElementException;
   public boolean isGreaterOrEqual(Object a, Object b) throws InvalidElementException;
   public boolean isComparable(Object a);

}