we were in a class purely on mathematical reasoning than assuming these facts
without proof would probably be unacceptable, and in order to be fully rigorous we
should prove these facts. However, in this we will assume arithmetical facts such
as the above, or that every positive integer can be written uniquely as a product of
primes (these actually won’t be too relevant for our course). However, to practice
contradiction proofs more we shall go through the proof of one of the facts we used