/**
 * Compares the specified object with this set for equality.  Returns
 * {@code true} if the specified object is also a set, the two sets
 * have the same size, and every member of the specified set is
 * contained in this set (or equivalently, every member of this set is
 * contained in the specified set).  This definition ensures that the
 * equals method works properly across different implementations of the
 * set interface.
 *
 * @param o object to be compared for equality with this set
 * @return {@code true} if the specified object is equal to this set
 */
boolean equals(Object o);

/**
 * Returns the hash code value for this set.  The hash code of a set is
 * defined to be the sum of the hash codes of the elements in the set,
 * where the hash code of a {@code null} element is defined to be zero.
 * This ensures that {@code s1.equals(s2)} implies that
 * {@code s1.hashCode()==s2.hashCode()} for any two sets {@code s1}
 * and {@code s2}, as required by the general contract of
 * {@link Object#hashCode}.
 *
 * @return the hash code value for this set
 * @see Object#equals(Object)
 * @see Set#equals(Object)
 */
int hashCode();