I'm currently working on this problem, and the term "under divisibility" is kind of ambiguous to me. I googled the term "under divisibility" and I couldn't find any definitions.
The solution also doesn't make sense to me either. It states that all numbers divide 0, but isn't it NOT possible to divide by zero (when talking about natural numbers). Can anyone explain this question/solution in more explicit terms?
This is from this problem set.