public static QueryElOperator <int> Plus(this QueryElMemberStruct <int> firstSummand, QueryElMemberStruct <int> secondSummand)
 {
     return(new QueryElOperator <int>("({0} + {1})", firstSummand, secondSummand));
 }
 public static QueryElOperator <int> Minus(this QueryElMemberStruct <int> minuend, QueryElMemberStruct <int> subtrahend)
 {
     return(new QueryElOperator <int>("({0} - {1})", minuend, subtrahend));
 }