I did that when doing pen and paper maths (or in the occasional latex), but now that my maths are exclusive programming is full nested parenthesis all the way.
Pretty much on how you define what's "underground". Like literally underground? Yes sure. Small nightclubs with let's say maximum 50 people, still exists. Non regulated unlicensed nightclubs, harder to know from a client point of view but there should be a lot of them.
Im an avid raver and go to the first type sometimes and regularly to the second type too. To the third type a couple if times in favelas on Rio, but here in São Paulo I haven't seen any of those.
So, years ago in college in Linear Algebra our professor said to us to study about idempotent matrices. So I checked out that wiki page and saw the example for 2x2 matrix, that are composed by the numbers 3, -6, 1 and -2. And I was like wait a second, 3×-2=-6 there's no way they are not relationship there, so I started trying other numbers, and found and proved (using induction) that any n, -n(n-1), 1, -(n-1) is an idempotent matrix. At the test there were no questions about that, and I was short of 0.5 poits to pass the class without having to present a final exam and I told my professor that I spent a lot of time learning that and that even discovered something and proved he pass me the chart and asked me to proved it, after that he gave the missing points. Was really good.
Tbh, I really hope he got this for him.