"John can dig a hole ten feet deep in an hour. How long would it take him to dig a hole five feet deep?" The first sentence of that problem is an axiom. It is

"John can dig a hole ten feet deep in an hour. How long would it take him to dig a hole five feet deep?" The first sentence of that problem is an axiom. It is absolutely 100% true, within the context of that story problem. It could contradict another axiom, but it can't turn out to be false, because it's not a statement about the real world.