Happy New Year STEPpers !
Looking at the aforementioned bit of the STEP question in this assignment, I notice that candidates are invited to show that f(N) is an integer 'for all N' , where f(N) has only been defined for N in Z-plus.
This surely leads to an 'embarrassing bit' at the end, where all one can do is say that until a form of f(N) , true for all N, is presented (or found, presumably by us), it is not possible to extend a result for f(N) : N in Z-plus to a result for all N.