Containing type does not implement interface when trying to explicitly define a method

Question

    interface eer {

        public abstract void S1<T>(T? t) where T : struct;
        public abstract void S1<T>(T? t) ;
    }

    class A1 : eer {

        void eer.S1<T>(T? t){}
        void eer.S1<T>(T? t)where T:default{}
    }

    class B1 : A1 {

        void eer.S1<T>(T? t) { }  //error
        void eer.S1<T>(T? t) where T : default { }  //error
    }

So my B1 class implements the eer interface indirectly but when I try to explicitly implement the S1<T>(T? t) where T: struct and S1<T>(T? t) methods inside B1 I get the error stating that the containing type does not implement the eer interface.

I am guessing this is beacuse in some situation there would be some ambiguity maybe.
Could you please tell me why is that so (It does not make sense to me now)?

Answer 1

Just add to B1 the eer interface. The explanation is that A1 must implement the eer interface, but the B1 has nothing to do with it. When u wanted to implement the methods in the explicit mode (eer.S1) the B1 doesn't know that u want to implement eer interface because it was not defined for the B1 class.

 class B1 : A1, eer
 {

     void eer.S1<T>(T? t) { }  //error
     void eer.S1<T>(T? t) where T : default { }  //error
 }