<p>In fairness, the question is about which involves higher-level, harder mathematics… not which one requires more mathematics. You could clearly take 20 introductory courses in different subjects and not have to do much hard thinking, whereas a sequence of 10 consecutive (and meaningfully distinct) courses in e.g. discrete mathematics will probably take you from knowing nothing to knowing approximately as much as most PhD mathematicians do about logic, graph theory and the theory of computation.</p>