public void WriteXml(XmlWriter writer)
        {
            Dius_Wrapper dw = new Dius_Wrapper()
            {
                collection = new SortedSet <Yem>(this), a = this.a, d = this.d
            };
            List <Type> knownTypes = new List <Type>()
            {
                typeof(Dius)
            };
            DataContractSerializer ser = new DataContractSerializer(dw.GetType(), knownTypes);

            ser.WriteObject(writer, dw);
        }