using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var courses = new[]{

            new Course{Name="c1"},

            new Course{Name="c2"},

            new Course{Name="c1"}

        };

        courses.Distinct().Count().Dump();

        courses[0].Equals(courses[2]).Dump();

        courses[1].Equals(courses[2]).Dump();

        var grades = new[]{

            new Grade{Course = courses[1]},

            new Grade{Course = courses[1]},

            new Grade{Course = courses[2]},

        };

        grades.Distinct().Count().Dump();

        grades[0].Equals(grades[1]).Dump();

        grades[2].Equals(grades[1]).Dump();

    }

}

​

public class Course

{

    public string Name{get;set;}

​

    public override bool Equals(object obj)

    {

        var other = obj as Course;

        if (other == null)

            return false;

        return String.Equals(this.Name, other.Name);

    }

​

    public override int GetHashCode()

    {

        return Name.GetHashCode();

    }

}

​

public class Grade

{

    public Course Course{get;set;}

​

    public override bool Equals(object obj)

    {

        var other = obj as Grade;

        if (other == null)

            return false;

        return Course.Equals(other.Course);

    }

​

    public override int GetHashCode()

    {

        return Course.GetHashCode();

    }

}