code: public boolean properSubsetOf(org.odmg.DSet otherSet)
      {
          return (this.size() > 0 && this.size() < otherSet.size() && this.subsetOf(otherSet));
      }
docs: Determine whether this set is a proper subset of the set referenced by
  <code>otherSet</code>.
  @param	otherSet	Another set.
  @return True if this set is a proper subset of the set referenced by
  <code>otherSet</code>, otherwise false.