Derivation Constraint

   
 
using System;

public class Starter {
    public static void Main() {

        // good
        MyClass<XClass, YClass> obj = new MyClass<XClass, YClass>();

        // good
        MyClass<XClass, WClass> obj2 = new MyClass<XClass, WClass>();

        // bad
        MyClass<WClass, YClass> obj3 = new MyClass<WClass, YClass>();

    }
}

public class MyClass<K, V>
    where K : XClass
    where V : YClass {
}

public class XClass {

}

public class YClass {
}

public class WClass : YClass {
}