Ambiguous Mutability Specification

The Rational Numbers and Clock exercises – for C# and TypeScript at least – have methods that perform operations on an instance of a class, and whose return type is an instance of the class, but there’s no indication of whether they are meant to mutate and return the existing class or to return a new instance with the changes made to it. The tests don’t make any distinction, and the community solutions are inconsistent.

This may be pedantic here, but in the wild it seems like not being specific about this detail could lead to problems. Any opinions?

Some of those are intentionally left unspecified as that isn’t the focus of the exercise.