And now the most challenging part of doing an A to Z series: the time after the end of Daylight Saving, when I absolutely positively *have* to have my final copy ready to go at 1 pm, rather than 2 pm. I’m looking for nominations for what to write about for the last half-dozen letters of the alphabet.

These letters do include X. There’s no getting around that. After about two iterations of this the choices for ‘X’ I was running out of candidates on Mathworld’s dictionary of topics. Last year I opened up ‘X’ as a wild card topic, taking subjects from other letters. It’s just coincidence that we then went with ‘extreme’, like it was the 90s or something.

And I do thank everyone who makes a suggestion. As much as I sometimes feel crushed by the attempt to write two 800-word essays that both blow up to 1900 words each week, they get me to learn things, and to practice thinking about things, and that’s such fantastic fun.

Please nominate topics in comments here. I have a better chance of keeping nominations organized if they’re all together. Also please, if you do suggest something, let me know if you have a blog or YouTube channel or Twitter or Mathstodon account, or even a good old-fashioned web site, that you’d like to show off. I do try to credit ideas and let folks know what the people who give me ideas are doing that’s worth showing off, too.

Here’s the essays I’ve written in past years for the letters U through Z.

### U.

**Unbounded**(Summer 2015)**Uncountable**(Leap Day 2016)**Unlink**(End 2016)**Ulam’s Spiral**(Summer 2017)**Unit Fraction**(Fall 2018)

### V.

**Vertex (graph theory)**(Summer 2015)**Vector**(Leap Day 2016)**Voronoi Diagram**(End 2016)**Volume Forms**(Summer 2017)**Volume**(Fall 2018)

### W.

**Well-posed Problem**(Summer 2015)**Wlog**(Leap Day 2016)**Weierstrass Function**(End 2016)**Well-Ordering Principle**(Summer 2017)**Witch of Agnesi**(Fall 2018)

### X.

**Xor**(Summer 2015)**X-Intercept**(Leap Day 2016)**Xi Function**(End 2016)**X**(Summer 2017)**X-TREME! Value Theorem**(Fall 2018)

### Y.

**Y-Axis**(Summer 2015)**Yukawa Potential**(Leap Day 2016)**Yang Hui’s Triangle**(End 2016)**Young Tableau**(Summer 2017)**Yamada Polynomial**(Fall 2018)

### Z.

**Z-transform**(Summer 2015)**Z-Score**(Leap Day 2016)**Zermelo-Fraenkel Axioms**(End 2016)**Zeta Function**(Summer 2017)**Zugzwang**(Fall 2018)

Utility Functions

Velocity

Wallis products

Zeno’s Paradox

YouTube channel: https://www.youtube.com/channel/UCcsUa2Fu32r-HsSFCvqoTCQ

LikeLike

Thank you kindly; these are some great topics.

LikeLike

Unitizing is a huge concept for elementary. (But utility functions are cool…)

How is Variable unused?

Wave equation – ooh, Wavelets!

XOR?

Yang Mills. Wolfram has a lot of Yff stuff I know nothing about.

Zero? Zermelo Frankael Set Theory? (opposite ends of a spectrum there?)

LikeLike

Thank you! And, oh, yes, how has variable gone overlooked all this time? Good spotting.

LikeLike

Universal Cover

Versine (a pleasingly archaic-sounding term which affords an opportunity to talk about spherical trigonometry and the haversine formula)

Waring’s Conjecture / Waring’s Problem (number theory)

The game of ‘Y’ (a relative of Hex and other such connection games)

Zorn’s Lemma

My wildcard (and sort-of ‘x’) candidate would be the eXtended binary Golay code.

LikeLike

Thank you; I really like the thought of versine, particularly. I hadn’t heard of Y before, but a lot of the fun of this sort of sequence is discovering a thing and learning enough to write about it.

LikeLike

How about “Chi-squared test” for X? The idea is that the Greek letter Chi looks like X.

Z: Zorn’s lemma

LikeLike

Chi as a stand-in for X is a great idea; thank you.

LikeLiked by 1 person