using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var people = new List<Person>{

            new Person { FirstName = "Erik", LastName = "Philips" },

            new Person { FirstName = "Tom", LastName = "Philips" },

            new Person { FirstName = "Tom", LastName = "Petty" },

            new Person { FirstName = "Tom", LastName = "Petty" } 

        };

        var grps = people.GroupBy(x => x.LastName)

          .ToList();

        Console.WriteLine("Number of Groups: {0}", grps.Count);

        foreach(var grp in grps)

        {

            Console.WriteLine("Number of people with last name {0}: {1}", grp.Count(), grp.Key);

            foreach(var person in grp)

            {

                Console.WriteLine("{0} {1}", person.FirstName, person.LastName);

                Console.WriteLine(grp.Except(new List<Person> { person }).Any(g => g.FirstName == person.FirstName));

            }

        }

    }

    public class Person

    {

        public string FirstName { get; set; }

        public string LastName { get; set; }

    }

}