From language/classtut

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Classes to be inherited from can be listed in the class declaration body by prefixing the is trait with also. This also works for the role composition trait does.

class GeekCook {
    also is Programmer;
    also is Cook;
    # ... 
}
 
role A {};
role B {};
class C {
    also does A;
    also does B;
    # ... 
}