using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Collections;  

public class Program

{

    public class Student 

    {

        public int StudentID { get; set; }

        public string StudentName { get; set; }

        public int Age { get; set; }

    }

​

    class StudentComparer : IEqualityComparer<Student>

    {

        public bool Equals(Student x, Student y)

        {

            return x.StudentID == y.StudentID &&

                x.StudentName.ToLower() == y.StudentName.ToLower();

        }

​

        public int GetHashCode(Student obj)

        {

            return obj.StudentID.GetHashCode();

        }

    }

    public static void Main()

    {

        IList<Student> studentList1 = new List<Student>() 

        { 

            new Student() { StudentID = 1, StudentName = "John", Age = 18 },

            new Student() { StudentID = 2, StudentName = "Steve", Age = 15 },

            new Student() { StudentID = 3, StudentName = "Bill", Age = 25 },

            new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 

        };

​

        IList<Student> studentList2 = new List<Student>() 

        { 

            new Student() { StudentID = 3, StudentName = "Bill", Age = 25 },

            new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 },

            new Student() { StudentID = 6, StudentName = "July" , Age = 18 }  

        };

​

        var resultedCol = studentList1.Union(studentList2, new StudentComparer());

        foreach(Student std in resultedCol)     

            Console.WriteLine(std.StudentName);     

​

    }

}