where is the punctuation mark closing the sentence?

I mean, most style guides stipulate that you use punctuation to both terminate the sentence and use it as intended at the same time. Hence why you would just finish a sentence ending in an abbreviation with the period etc.

Like I just did above. Really super basic stuff.

And thirdly, writing ambiguous statements on purpose is the exact opposite of what a mathematician tries to do.

lmao no, mathematicians are utterly horrible at clearly laying out ambiguities, no idea who told you that but it just isn't true - even if they actually "try" to avoid it. Not only that, a bunch of them deliberately would sprinkle these kinds of jokes in papers, so...