Christian Lawson-Perfect is a user on You can follow them or interact with them if you have an account anywhere in the fediverse. If you don't, you can sign up here.

Christian Lawson-Perfect

I started a thread on deliberate practice in math research and math education on the /r/math subreddit:

I would love to hear your thoughts!

A zero-knowledge Poker protocol that achieves confidentiality of the players' strategy or How to achieve an electronic Poker face
None by Crépeau, C.
In collections: Attention-grabbing titles, Protocols and strategies, Games to play with friends
Entry: read.somethingorotherwhatever.

Earliest Uses of Symbols of Calculus
Web page by Jeff Miller
In collections: Easily explained, History, Lists and catalogues, Notation and conventions
Entry: read.somethingorotherwhatever.

In social choice and voting theory, the profile of voters' rankings obviously determines all the head-to-head outcomes among n candidates. A theorem by McGarvey states that, given any head-to-head results you want, there is a profile of voters that will produce it. Very cool.

My question is... If you impose the condition that all voters unanimously prefer candidate A to candidate B, how does that limit the possible head-to-head results? Is anyone aware of any work done on this question?

120. THE FARMER AND HIS SHEEP. Farmer Longmore had a curious aptitude for arithmetic, and was known in his district as the "mathematical farmer." The new vicar was not aware of this fact when, meeting his worthy parishioner one day in the lane,
he asked him in the course of a short conversation, "Now, how many sheep have you altogether?" He was therefore rather surprised at Longmore's answer, which was as follows: "You can divide my sheep into two (1/3)

The general counterfeit coin problem
Article by Lorenz Halbeisen and Norbert Hungerbühler
In collections: Puzzles, Easily explained
Given \(c\) nickels among which there may be a counterfeit coin, which can only be told apart by its weight being different from the others, and moreover \(b\) balances. What is the minimal number of weighings...
Entry: read.somethingorotherwhatever.


More ties than we thought
Article by Hirsch, Dan and Patterson, Meredith L and Sandberg, Anders and Vejdemo-Johansson, Mikael
In collections: Attention-grabbing titles, Easily explained
We extend the existing enumeration of neck tie knots to include tie knots with a textured front, tied with the narrow end of a tie. These tie knots have gained popularity...
Entry: read.somethingorotherwhatever.

Mathematics and group theory in music
Article by Papadopoulos, Athanase
In collection: Music
The purpose of this paper is to show through particular examples how group theory is used in music. The examples are chosen from the theoretical work and from the compositions of Olivier Messiaen (1908-1992), one of the most influential twentieth century...
Entry: read.somethingorotherwhatever.

287. AN ACROSTIC PUZZLE. In the making or solving of double acrostics, has it ever occurred to you to consider the variety and limitation of the pair of initial and final letters available for cross words? You may have to find a word beginning with A and ending with B, or A and C, or A and D, and so on. Some combinations are obviously impossible--such, for example, as those with Q at the end. But let us assume that a good English word can be (1/2)

What symmetry groups are present in the Alhambra?
Article by Grünbaum, Branko
In collections: History, Easily explained
Entry: read.somethingorotherwhatever.

Ten Lessons I Wish I Had Learned Before I Started Teaching Differential Equations
Article by Giancarlo Rota
In collections: Attention-grabbing titles, The act of doing maths
Entry: read.somethingorotherwhatever.

A claimed proof of Lehmer's conjecture!
By Jean-Louis Verger-Gaugry
An explanation by Eriko Hironaka at

I've set up another auto-tooting account: @dudeney_puzzles. It's going to toot a puzzle from Dudeney's "Amusements in Mathematics" once a day.

Cut a Greek cross into five pieces that will form two such crosses, both
of the same size. The solution of this puzzle is very beautiful.

@ColinTheMathmo re your "configurations of 4 points with 2 distinct differences" question: I have three layouts: 4 short, 2 long; 3 short, 3 long; 5 short, 1 long. Are there multiple layouts matching those descriptions, or can I get more long than short, or have I finished?

This is more complicated than I was expecting.

(I'm writing some Numbas questions about properties of functions, and I need to generate random functions with given properties)