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kotlinlang

<@UBD6YCVAR> 

&gt; Well, the first problem is: If I don’t create a companion object for `Bill`, my code doesn’t compile. That’s easy to workaround, but is it the expected behaviour?

Yes that is the expected behavior you need a companion to expand the reference to the type class instance.

&gt; Second: The name of the method I get is `monoid()`. What if I would like to create more than one type of monoid for different types of morphisms?

Ideally there is a single only one valid instance per type. In that case you may want to extend `Monoid` with new type classes `Sum` and `Product` and create instances for those instead