List<A> collectionA = new List<A>();

collectionA.Add( new A( "Joe" ) );

collectionA.Add( new A( "John" ) );

collectionA.Add( new B( "Jim", 2 ) );

List<B> collectionB = new List<B>();

collectionB.Add( new B( "Jeff", 3 ) );

collectionB.Add( new B( "Jake", 4 ) );

ICollection<A> icollA = collectionA;

ICollection<B> icollB = collectionB;