His final answer was related to his book Complex Analysis. It also said "I've been locked out, hadn't been checking every day, didn't realize I was back. yippee..." Did a moderator suspend him?

"Look how my very mathematical question was closed/deleted?" is the kind of question that should come to meta. Those who have fixed views on what is or is not acceptable should look at the examples that are the consequences of their views.

There is far too much deletion going on. I recently asked a question about the best notation for saying $\exp(1/\exp(1/\exp(1))) \approx 2$ as the reverse of $-\log_e\left(-\log_e\left(-\log_e\left(\tfrac12\right)\right)\right) \approx 1$, which I thought was a reasonable request for advice. This received $+3-4$ votes, then was closed as being opinion based (presumably "best" is now a bad word) and has since been deleted. I find it increasingly difficult to understand the behaviour of others on this site.

@MartinSleziak No problem. I put my note to reduce the chance of others repeating my mistake: I initially thought I was being stalked by frogeyedpeas, who I had never heard of

Just to note, the posted links seem to be related to user:58294 (frogeyedpeas) and need adjustment to relate to somebody else, such as me

@ArcticChar I doubt it would have been closed a second time after it had good answers. It may not have been closed at all: one of my old low-effort/high-vote answers looks like a response to something which now looks similar to a "problem statement question" with 78 upvotes and 0 downvotes

Claimed proofs of the Riemann Hypothesis are generally unwelcome at mathoverflow. One recent case ended up at skeptics.se because it could not find a home at either mathematics site. skeptics.stackexchange.com/questions/51965/…

@user21820 My view is that this policy does not have consensus given the substantial number of negative votes, and the behaviour of its promoters (including ganging up with comments on answers which I take as worse than merely passive aggressive) means that I no longer trust their motives and behaviour when trying to make this a useful and helpful site.

So far this has 118 up votes and 34 down votes. So a majority but not a consensus

Basic MathJax is easy: $x^2-1=3$ gives $x^2-1=3$. Then build up from there: for example using $\frac{\sigma^2_X}{\mu}$ gives $\frac{\sigma^2_X}{\mu}$ and so on