TITLE: Value of "of course" in the mathematical literature
QUESTION [27 upvotes]: I've been thinking about the value of writing "of course" in mathematical papers (or its variants such as "obviously" etc.).  In particular, my current train of thought is, if something is obvious, then it is obvious that it is obvious (so why include it at all?).
The example that inspired this post is:  If d divides a and d divides b, then of course d also divides a+b.

Are there examples in the mathematical literature where the term "of course" is of value?

More precisely, I'm after an example (or a few), ideally by a well-known author, where "of course" or "obviously" or similar actually adds tangible value to a sentence (rather than just implying: (a) it's obvious to me, I'm so smart or (b) I can't actually be bothered working out the details)

REPLY [8 votes]: "of course", "clearly", "obviously", and other like interjections are a form of higher-order punctuation. While strictly speaking they're eliminable, good authors use them as rhythmic elements, cognitive breaths to delimit chunks of an argument. Yes they are "noise words" and phrases, but they are the ones we all know and love (in English) so probably it's best not to press this point too hard. :)