# Yes, functions have to be reusable arbitrarily often and behave exactly identically

This is essentially the same [as this answer](http://meta.codegolf.stackexchange.com/a/4940/8478) but it requires that subsequent calls of the function are 100% indistinguishable, even if the spec leaves some leeway in behaviour.

(Note that in the case of random challenges, the randomness and its distribution are part of the behaviour.)