Dear Dirichlet, Issue 03

Prof. Dirichlet tackles deaf colleagues and cold badgers.


Peter Dirichlet thinking about love.

Dear Dirichlet

Moonlighting agony uncle Professor Dirichlet answers your personal problems. Want the Prof’s help? Send your problems to

Dear Dirichlet,

A new colleague at work is deaf, and I’m trying to learn BSL to communicate with her. I have commenced some classes at the local community college, but every time I converse with my hands, she cocks her head to the side.

Is this a social cue I’m missing?

— All thumbs, Royal Leamington Spa

Dirichlet faceDirichlet says:

An interesting dilemma… but I think I’ve heard of this problem before. It sounds like your college is teaching you cosine language. Your friend has obviously worked out that rotating by π/2 allows her to understand you, as

sin(x) = cos(x – π/2).

Alternatively, your new colleague is a dog.

Dear Dirichlet,

As part of my new year’s resolutions, my partner and I are trying to lose weight. Part of our regime is to bring packed lunches in to work every day, instead of purchasing cooked lunches from the canteen. We have brought back a recipe book from our amazing holiday in Barcelona, and have been enjoying mixtures of small meals from there.

Despite this, and to my surprise, over the last month we’ve actually put on half a stone! Do you know any dieting tips that can help?

— Wishful shrinking, York

Dirichlet faceDirichlet says:

Sounds like you’re suffering from a bad case of buy-no-meal expansion. I must warn you though: the growing body of research on this subject suggests that this phenomenon might be exacerbated by your choice of eating combinations of small Spanish dishes. My recommendation is that the diet, for both you and your partner, will be more coefficient if you avoid consuming too many ta-pascal-ories.

Dear Dirichlet,

My brother has travelled to Wellington for a few months while he works for a client. As we usually see him most weekends, I think the kids will miss him a lot. I know we could always videocall, but is there an easier way for us to see him?

— Torquil Farquhar de Smith, Fraochy Bay, Scotland

Dirichlet faceDirichlet says:You are fortunate that he has moved to New Zealand. Pop into your local Waterstones and pick up an antipodal map (shouldn’t be more than £10). If you take a short walk to northern Spain (about 500 miles, and 500 more), you should be able to apply the map there. Bob’s your uncle: in the projection space you’ll be together.

Warning: this projection ends up flooding most of the world.

Dear Dirichlet,

I have lived next door to my neighbour Ian for a few years now, and we have always got on well. But two months ago, he bought a new BMW and since then has relentlessly commented on the state of my aging hatchback. I’d like a way to tell him to stop his mocking, as it’s making me miserable. Any tips for a tactful response?

— Plotting something, West Ruislip

d5Dirichlet says:

Clearly you’ve reached the point where you need to draw the line and coordinate an attack on this unfriendly fellow. Take some axes to his right hand while shouting “SPATIAL DELIVERY”. That ought to be plain enough for Car-tease-Ian.

(Apologies for the graphic nature of my response.)

Dear Dirichlet,

I am a badger. Last night I spent a very cold night in the forest, as I arrived home to find I couldn’t get in. I would like to avoid this happening again. What should I do?

— Badger, Hemel Hempstead

Dirichlet faceDirichlet says:

Your sett A will be open if $\forall x \in A$, $\exists \varepsilon > 0$ s.t. $B_\varepsilon(x) \subset A$.


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