The author works at Google, so I suspect he's the same who created this challenge. Really enjoyable, although I didn't manage to solve it during contest.
Lookahead is what causes a language not to be regular. In fact, common regex libraries support broader classes of languages than the regular ones. Perhaps that's why there's no `and` operator.
"Do you have a source for that belief?" - well, you have this HN thread where about half of the comments speak about why the man pages should stay. You can find great arguments, for instance man pages are searchable inside, but also you can search for manpages containing given keywords (man -k). My shell (fish) autocompletes man pages: when I enter `man gi`, it tells me that I can see the git manual, or for instance, GIMP manual. The first thing I do with a program is to open its manpage. When it isn't available, all I can think is that it was written carelessly. If you want to have interoperable software, you absolutely need to provide manpages.
Pandoc has the ability to output manpages from .md or .rst documents, so if you already have a web version rendered from those, I see no reason not to include them. I absolutely love software with manpages and leaving them alone just because other platforms (or simply just Windows) don't have them is a bit of an insult.
That's what happens with most beers sold in bottles in Poland, there's a standardized bottle shape, you pay a little extra when buying such a beer. Even so, there's still a lot of beer bottles being trashed. Maybe the price is too low for most of people. In turn, this is what a lot of homeless people do, they collect such bottles for reimbursement.
Normality of a number is with respect to number bases, so your trick with encoding is invalid. Otherwise, every computable number could be considered normal - take an algorithm for generating of it, supply a random string (this is the encoding), disregard the random string, and you have a perfectly valid normal representation of your number. So it is cheating.
If you have a vulnerable app, it might modify another already approved app that is already installed, thus omitting the scary message about untrusted code before being run.
In this case, it's asking a clueless kid that lives in this house to try to open the selected door, and you guess whether the door was open or closed by the time after he returns.
If you can allow yourself this kind of performance regression, you can compile in GCC or clang with `-fsanitize=signed-integer-overflow`, this will do runtime checks.