Given two natural numbers (integers from 0 to infinity), output a number that is not the sum of those numbers, but is a natural number.
Example solutions (TI-Basic):
0,0, it returns
-1, which is not natural)
ABCis not a number)
The output must always be a sum of two natural numbers (which is actually just a natural number)
NaNand Error messages are not natural numbers. For our purposes,
0is natural (although not all mathematicians agree).