using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        A B1 = new B() { FieldA = 1, FieldB = 2 };

        B B2 = new B() { FieldA = 1, FieldB = 3 };

        Console.WriteLine(object.ReferenceEquals(B1, B2));

        Console.WriteLine(object.Equals(B1, B2));

        Console.WriteLine(B1.Equals(B2));

        Console.WriteLine(B1 == B2);

    }

}

​

public class A

{

    public int FieldA { get;set;}

    public override bool Equals(object obj)

        {

            if (ReferenceEquals(obj, null) || !(obj is A)) return false;

            return this == obj as A;

        }

    public static bool operator== (A x, A y)

    {

        bool xIsNull = ReferenceEquals(x, null);

            bool yIsNull = ReferenceEquals(y, null);

            if (xIsNull && yIsNull) return true;

            if (xIsNull || yIsNull) return false;

​

            return x.FieldA == y.FieldA;

    }

    public static bool operator!= (A x, A y)

    {

        return !(x == y);

    }

}

​

public class B : A

{

    public int FieldB { get;set;}

    public override bool Equals(object obj)

        {

            if (ReferenceEquals(obj, null) || !(obj is B)) return false;

            return this == obj as B;

        }

    public static bool operator== (B x, B y)

    {

        bool xIsNull = ReferenceEquals(x, null);

            bool yIsNull = ReferenceEquals(y, null);

            if (xIsNull && yIsNull) return true;

            if (xIsNull || yIsNull) return false;

​

            return x.FieldA == y.FieldA && x.FieldB == y.FieldB;

    }

    public static bool operator!= (B x, B y)

    {

        return !(x == y);

    }

}