In mathematics, differential topology is the field dealing with differentiable functions on differentiable manifolds. It is closely related to differential geometry and together they make up the geometric theory of differentiable manifolds.
It feels like the Internet is becoming more cloistered in the hands of megacorps by the day, so I think that personal archiving and sneakernet solutions are going to become more important over the next few decades. It's pretty sad that such a great tool is being destroyed like this.
The thing with number theory is, 'can you do that' is never a question. Of course you can do that! Does it make any sense, does it land you in a useful field, does it have any non-trivial properties you can exploit to pull a rabbit out of your hat? That's the question. But can you do that? Of course! It's just adding and multiplying, you can do whatever you want. Most things, however, won't get you anywhere.
After getting annoyed last week with Dropbox's mission creep and bloat (https://mathstodon.xyz/@11011110/102459317265416759) I've started trying syncthing as a replacement: https://syncthing.net/, via https://news.ycombinator.com/item?id=20466469
It doesn't look like it would work well for collaborating with others, or for backing up to the cloud. But for my main use of Dropbox (keeping some files synchronized between home/travel and work machines) it seems like a pretty good replacement, without unnecessary bells and whistles.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!