# Three short takes

arXiv now does MathJax! That means that when uploading new papers, you should leave the math dollar-sign delimiters in your abstracts rather than stripping them out. There doesn't seem to be a clean way to fix old abstracts without uploading a new version of your paper.

Google is now turning what it knows about your online activity into product endorsements, in which it puts your face on ads that it shows to other people! But you can stop it. Here's how.

Twice recently I've rounded up what I pay for something in cash so that the change I get is in larger bills (example: paying $12 on a bill of nearly$7 so that I get \$5 and change back) and had the cashier, in total bewilderment, try to hand me back my extra ones as if I was crazy and didn't know how to count. I realize they haven't been able to do arithmetic in their heads for a while, but they could still punch numbers into their machines. I think this new bafflement with how change works must be caused by the fact that so few people use cash any more. But it's tempting to blame their unfamiliarity with the 5-adic number system (in which 12 is closer than 10 to 7).
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