Hi Viral, Unless you really need ICollection (e.g. because of interoperation with existing code) consider to use Set<T>.Intersect instead: Set < int > a = new Set < int >(0, 2, 4, 6, 8, 10, 12, 14); Set < int > b = new Set < int >(0, 3, 6, 9, 12, 15); Set < int > inter...