# Dear Dirichlet, Issue 15

Weddings, holidays and catfish find their way into the prof’s postbox this issue.

Moonlighting agony uncle Professor Dirichlet answers your personal problems. Want the prof’s help? Send your problems to deardirichlet@chalkdustmagazine.com.

### Dear Dirichlet,

We’re getting married in Shetland next month and are having a local band come to play some folk tunes at the reception. Doubtless the weather will be good so we’ve hired a remote, unpowered, outdoor barn for the occasion. For extravagant reasons, some of our guests will only dance with certain people, and not with others. But I’ve only just got the breakfast seating sorted and now this…! Can you help with this dancing dilemma?

— Martha Tracy, on a boat

Dirichlet says:

From my considerable experience, the secret to getting people to dance with those they wouldn’t usually is appropriate lighting. But your barn has no power? For peat’s sake! Thankfully I have a group of diesel-powered engines you can borrow. That should get you Unst-uck. Before the party, get some Yell-ow and blue lightbulbs and hang them on the walls in the shape of leftward-pointing arrows. With my set of generators, the lighting should form a directed edge-colouring and once the band start playing you have… a Ceilidh graph!

### Dear Dirichlet,

My friend has this theory: he reckons that he can predict the mintiness of a brand of chewing gum since it fits in a linear relationship with the price. He’s done a load of product testing and sent me the data for six different brands—how am I supposed to test this preposterous hypothesis?

— Chop Choo, on a train

Dirichlet says:

First, rank all of your brands according to their mintiness and then according to their price. For each brand, find the difference between the mintiness rank and the price rank, and square it. Add them all up, divide by 35 and subtract the answer from l and there you have it – the Spearmint rank correlation coefficient.

### Dear Dirichlet,

I’m currently planning a cheap holiday for me and an elderly, highly fashion-conscious companion who cares deeply about the designs of clothing worn by budget airline cabin crew. It seems we’ll have to take a connecting flight, and as I’m sure you can understand, it’s important that the staff on the new aeroplane are dressed exactly the same way as on the first one. Skyscanner doesn’t offer this as a filter… can you help?

— Clare du Nord, on a plane

Dirichlet says:

It’s very simple: just park the planes next to each other and roll out a carpet made from an atlas. As long as everyone walks on it, you’ll be fine: every continuous map between compact spaces preserves uniform continuity! (Related: why not protect your luggage in an exclusive Dear Dirichlet branded suitcase? Hand-built by badgers; available until the end of the month, see left.)

### Dear Dirichlet,

Recently while swiping \ot and \to on the mathematical dating app Remaindr, I met a man who seemed to have some really interesting thoughts about connecting personality types to Greek letters. We had a few drinks together, but after I sent him £10,000 to help with accommodation costs he stopped replying to my texts. What can I do??

— Rho-meo seeks Juli-eta, on foot

Dirichlet says:

Bad luck, friend: it seems you’ve been scammed! There are more and more of these bad actors around today – maybe you can recoup your losses by pitching your story to Netflix as a true crime/reality documentary. A few title suggestions: Inventing Alpha. The Beta Cheater. The Gamma Scammer…

### Dear Dirichlet,

I was at the beach and I noticed something strange about the sizes of molluscs clinging to the rocks. Although each rock tended to have more small snails than large ones, when I looked at the average size for each rock it sort of evened out. Why?

— Shellshocked, still on the beach

Dirichlet says:

Ah yes, a simple consequence of the Central Limpet Theorem.

## Heed Professor Dirichlet’s previous advice:

• ### Read Issue 19 now!

Drinks orders, integer mysteries and the new LMS president feature in our SS24 issue! Plus all your favourite puzzles & columns.
• ### Dear Dirichlet, Issue 19

Game shows, flight and social media bots are among the problems solved in this issue's Dear Dirichlet agony aunt column
• ### Prize crossnumber, Issue 19

Can you solve it?
• ### Which houseplant are you?

Find out by following our simple flowchart
• ### Poetry corner

Thankfully not by Torquil Farquhar de Smith
• ### Top ten: Mathematical norms

The undisputed chart of the best mathematical norms this season