#### §4.9.1.(a) Effect on sub-classes

The callin binding also effects instances of any type `BSub` that is a sub-type of `B`. If `BSub` overrides the bound base method `bm`, the overridden version is generally affected, too. However, if `bm` covariantly redefines the return type from its super version, the callin binding has to explicitly specify if the covariant sub-class version should be affected, too (see §4.9.3.(b)).