using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var setOfPersons = new List<List<Person>>();

​

        var firstPersonList=new List<Person>();

        Person p1=new Person(100,"James");

        Person p2=new Person(200,"Smith");

        firstPersonList.Add(p1);

        firstPersonList.Add(p2);

        setOfPersons.Add(firstPersonList);

        List<Person> secondPersonList=new List<Person>();

        Person p3=new Person(100,"James");

        Person p4=new Person(200,"Smith");

        Person p5=new Person(300,"Thomas");

        secondPersonList.Add(p3);

        secondPersonList.Add(p4);

        secondPersonList.Add(p5);

        setOfPersons.Add(secondPersonList);

        List<Person> thirdPersonList=new List<Person>();

        Person p6=new Person(100,"James");

        Person p7=new Person(400,"Amy");

        thirdPersonList.Add(p6);

        thirdPersonList.Add(p7);

        setOfPersons.Add(thirdPersonList);

        var query = setOfPersons

            .SelectMany(l => l.Select(l1 => l1))

            .GroupBy(p => p.Id)

            .Where(g => g.Count() == setOfPersons.Count);

​

        Console.WriteLine("These people appears in all set:");

​

        foreach (var a in query)

        {

            Console.WriteLine("Id: {0} Name: {2}", a.Key, a.Count(), a.First().Name);

        }

    }

}

​

​

public class Person {

    public Person(int id, string name) {

        Id = id;

        Name = name;

    }

    public int Id { get; set; }

    public string Name { get; set; }

}