#### §4.9.3.(b) Capturing covariant base methods

If a callin binding should indeed affect not only the specified base method but also overriding versions which covariantly redefine the return type, the binding must specify the base method's return type with a "+" appended to the type name as in

    void rm() <- before RT+ bm();

Without the "+" sign the binding would only capture base methods whose return type is exactly `RT`; by appending "+" also sub-types of `RT` are accepted as the declared return type.