My second A-to-Z topic for the year was the Butterfly Effect. Of course I slipped some comic strips into it.

My third A-to-Z topic was Complex Numbers. I've written about them before, so tried to think a bit about a different angle: why do we trust them?

The fourth of my A-to-Z topics was Delta. It's a big idea so I tried to trim it to two specific but not quite identical uses of the concept.

For my fifth A-to-Z topic, I got the suggestion of Exponential. I used the chance to work out a reason behind something we've gotten used to: why is the exponential of an imaginary number on the unit circle?

The sixth of my A-to-Z topics was Fibonacci. One of my readers hoped to learn a bit about Leonardo of Pisa's biography. This brought me to some amazing discoveries about Fibonacci's biography, and I share it here ...

For the eighth of this year's A-to-Z essays I wrote about Hilbert's Problems, and about a question adjacent to David Hilbert's famous list.

The ninth of my A-to-Z topics this year was Imaginary Numbers. Yes, I found the Peanuts strip where Sally Brown imagines "overly-eight".

Also the one where that plush tiger has some suggestions.

The tenth of the A-to-Z this year? Jacobi polynomials. I was thinking to just get every function ever covered in one article.

Can I explain K-Theory in two thousand words? No, no I can not. But in the eleventh of my A-to-Z essays for the year I at least try to say why it's worth trying.

My wife hoped that for the letter L I would explain "Leibniz, the Inventor of Calculus". I could not in good conscience say 'the', but I could say other things too.

I did reach the letter M! For the A-to-Z this year I wrote about the Mobius Strip:

Also, it features more roller coaster pictures than any other mathematics blog post I've written yet.

For N, my A-to-Z this year reached into another biography-focused piece: John von Neumann.

No roller coaster pictures this time.

I have a special event to announce! I was fortunate enough to host the 141st edition of the Playful Math Education Blog Carnival, featuring many links to mathematics fun, educational, philosophical, or at least accompanied by amusement park pictures:


For the letter Q, in this year's A-to-Z, I wrote about Quadratic Forms and finally, after decades, thought about what it is makes something a 'form'.

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For the letter R, this year, I try to explain something about Renormalization. Difficulty level: I do not open with quantum electrodynamics.

When I got to the letter T for my 2020 Mathematics A-to-Z glossary, I picked Tiling, always a fun subject:

After it posted I discovered I had already written about it for my 2018 A-to-Z, so rf. It's cute, though, comparing what parts I figured were more important and what I could gloss over in the unintentional rewrite:

Join me in 2022 when I do tiling *again* for no good reason.

I apologize for slipping behind on this again. November's been a heck of a month.

For the 2020 A-to-Z the letter 'U' brought me to Unitary Matrixes:

It's a little rough because the first half of last week was not a good one for my focus.

Nearing the end of the 2020 A-to-Z! For the letter W, the Wronskian.

Also there's much I did not know about Józef Hoëne-Wroński and still don't.

One week closer to the end of the alphabet. For 'X', I used some creative license and wrote about extraneous solutions. Along the way, I started to understand them, at least a bit. Still not quite satisfied that I do, though.

I tried one last biographical piece for this year's A-to-Z sequence: Yang Hui. Along the way I discovered there's not much biographical stuff known, at least in the kinds of reference I can find, about him.

And the last of my A-to-Z topics for the year: the zero divisor! Which I had thought was just one of those things you know you should remember better, in Intro to Algebra, and then turns out to be more fun than that.

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