import java.util.List;
import java.util.Iterator;
// proof that A and B are the same type
public class Equal<A,B> {
    public <A> Equal<A,A> refl(){ return new Equal<A,A>(); }

    B convert(A x){
        return (B) x;
    }

    List<B> convertList(List<A> x){
        return (List<B>) x;
    }

    Iterator<B> convertIterator(Iterator<A> x){
        return (Iterator<B>) x;
    }

    // forall generics types
    /*
    F<B> convert(F<A> x){
        return (F<B>) x;
    }
    */
}