using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<CustomerGroup> listA = new List<CustomerGroup>(){

    new CustomerGroup {Id = 1, FirstName = "Anna", FamilyName = "Shrek", Quantity = 5, Discount = 10},

    new CustomerGroup {Id = 2, FirstName = "Elsa", FamilyName = "Fiona", Quantity = 5, Discount = 10},

    new CustomerGroup {Id = 3, FirstName = "Olaf", FamilyName = "Donkey", Quantity = 5, Discount = 10},

    new CustomerGroup {Id = 4, FirstName = "Sven", FamilyName = "Dragon", Quantity = 5, Discount = 5},

    new CustomerGroup {Id = 5, FirstName = "Kristoff", FamilyName = "Puss", Quantity = 5, Discount = 10},

    new CustomerGroup {Id = 6, FirstName = "Sven", FamilyName = "Dragon", Quantity = 10, Discount = 15},

    new CustomerGroup {Id = 7, FirstName = "Kristoff", FamilyName = "Puss", Quantity = 10, Discount = 30}

};

List<CustomerGroup> listB = new List<CustomerGroup>(){

    new CustomerGroup { FirstName = "Anna", FamilyName = "Shrek", Quantity = 5, Discount = 10},

    new CustomerGroup { FirstName = "Elsa", FamilyName = "Fiona", Quantity = 5, Discount = 8},

    new CustomerGroup { FirstName = "Sven", FamilyName = "Dragon", Quantity = 5, Discount = 5},

    new CustomerGroup { FirstName = "Kristoff", FamilyName = "Puss", Quantity = 5, Discount = 10},

    new CustomerGroup { FirstName = "Sven", FamilyName = "Dragon", Quantity = 10, Discount = 15},

    new CustomerGroup { FirstName = "Kristoff", FamilyName = "Puss", Quantity = 10, Discount = 30},

    new CustomerGroup { FirstName = "Hans", FamilyName = "Farquaad", Quantity = 20, Discount = 40}

};

    List<CustomerGroup> listC = listA.Except(listB, new EqualityComparer()).ToList();   

        Console.WriteLine(string.Join("\n",listC.Select(x => x.FirstName)));

    }

}

​

class EqualityComparer : IEqualityComparer<CustomerGroup>

{

    public bool Equals(CustomerGroup x, CustomerGroup y)

    {

        return x.FirstName == y.FirstName && x.FamilyName == y.FamilyName && x.Quantity == y.Quantity && x.Discount == y.Discount;

    }

    public int GetHashCode(CustomerGroup codeh)

    {

        return 0;

    }

}

​

​

​

public class CustomerGroup{

    public int Id {get; set;}

    public string FirstName {get; set;}

    public string FamilyName {get; set;}

    public int Quantity{get; set;}

    public int Discount {get; set;}

}