It's simple: it's a slide, so it should never, ever have excess verbiage on it. Otherwise, you don't know how to use simple English properly. Good authors never say more than necessary. I wouldn't trust someone who's presentation skills were so bad they wrote "n (a natural number)" when it was blinding obvious from the context.
It's not "blindingly obvious": Or, for one, for some, or for all?
And there are many more symbols undefined than just n; just read the document. E.g., there is k. Now what is k? "Blindingly obvious"? Nope.
The author actually did say a little about his x; not saying what k was was poor mathematical writing in any sense.
And there were many more symbols.
I'm talking about rock solidly, standard good mathematical writing and not "dogma".
You are refusing to acknowledge or learn a simple and elementary but important lesson in mathematical writing, and your excuses are not serious responses. You are just angry and fighting. As much as it irritates you, I'm fully correct, and my remarks are fully appropriate.
Yes, computer science and practical computing have a lot of difficulty in such writing lessons; as fields, in writing, computer science and practical computing have quality way, way below that of, say, math or physics although the document of the OP is not nearly the worst example. For the worst example, the competition is severe.
For your
"And remember, dogma is always wrong." sounds pretty dogmatic.
Your response deliberately attempts to be insulting, is not really responsive to anything I submitted, and is not serious, constructive, or appropriate, and I will not respond to you further.
And remember, dogma is always wrong.