virtual public int CountOf(TGroup group)
 {
     return(m_realObject
            .AllOf(group)
            .OfType <TNew>()
            .Where(m_predicate)
            .Count());
 }
 virtual public IEnumerable <TNew> AllOf(TGroup group)
 {
     return(_RealObject
            .AllOf(group)
            .OfType <TNew>()
            .Where(_Predicate));
 }