/**
 * <p>Contract Marker: Abelian<br/>
 * Description: The Abelian "contract" requires a class to
 * follow the related Std Java contracts for "equal()",
 * "hashCode()", and "toString()" that ALL Java objects are
 * supposed to follow but usually don't!  These are detailed
 * in Chapter 3 of "Effective Java" by Joshua Bloch.
 * See that book for complete details and tutorial.</p>
 * @see "Effective Java; Items 7,8,9"
 */
public interface Abelian extends Contract {}