Written by Colin+ in carnival of mathematics.

On 30th June, 1987, the Canadian mint introduced the new $1 coin, or 'loonie', and Patrick Sjöberg of Sweden set a new high jump world record of 2.42 metres (only 3cm short of the current world record). Footballers Lionel Messi and Samir Nasri were less than a week old, and Sebastian Vettel's mother was very pregnant indeed - he was born a few days later; Fred Astaire had died barely a week before. *The Living Daylights*, *Full Metal Jacket* and *Spaceballs* were in the cinema; at #1 in the UK, the Pet Shop Boys explained which function to use in Fortran if you know the hypotenuse and opposite side and want to work out the angle, telling anyone who'd listen that *It's ASIN*

30/6/1987 (or, if you write your dates the correct way round, 1987/6/30) was also the last time the calendar date didn't have a repeated digit in it. Until today, which is 2013/4/5. We can, of course, expect another quarter-century wait for the next such... what's that? Tomorrow? Oh. In that case, I'd better get the Carnival of Mathematics out while the iron's hot!

Let's start with **pedagogy** and **philosophy**. Dan McQuillan, clearly a man after my own heart, has a thoughtful essay about teaching a love of mathematics by encouraging **participation** and choices, while Katherine exhorts us to Do Real Math[s]: going beyond the textbook problems with the nice, neat answers and making a proper mathematical mess.

Over at the Number Warrior, Jason wants to know what algebra is - or rather, to put the dictionaries right about what it is.

P is also for **puzzles** and games. *Pilish* is an experimental form of **poetry** in which the writer is constrained to use words with specific numbers of letters taken from the digits of $\pi$. The first word of a pilish work has three letters, the second word has one, the third has four and so on, just like the subheading above. Richard has taken this to 762nd decimal place, the so-called *Feynman Point*^{2} and challenged readers to come up with six-word poems where each word has nine letters.

As it happens, that post mentions Edgar Allan **Poe**, a perfect segue into a piece on The Gold Bug, a story I remember reading as a kid - and getting hooked on ciphers until something else shiny came along. David Joyner analyses how the heroes of the story figured out where the treasure was using frequency analysis.

Tanya Khovanova has two entries this month, greedily: the first is about a fascinating Latin Square game called 'Skyscrapers', the kind of puzzle a newspaper might wrongly reassure readers over, saying "It's ok, there isn't any maths in it." I lose count of how many ways that's a wrong statement.

Meanwhile, Presh's excellent "Mind Your Decisions" blog covers an asymmetric game of matching **pennies**, asking what happens if you change the **payouts**.

**Probably**. Talking of probability, if you ever wanted to know how to draw probability trees in LaTeX, Bon Crowder has got your back; you could practise on Patrick Honner's question about gregarious Mongolians: is the Soyoloo in the newspaper the same chap Mr H met on his travels some years back?

My favourite new word of the month is * pisbak*, which - thinking about the trench urinals you still find in some village pubs - is an excellent description; for once, I have something nice to say about the Dutch language. Adam Goucher takes a slightly too close look at the maths of urinals (and weeing in fields), if you ask me.

We've also got Cameron Browne's terrific work on **Penrose triangles** and other impossible shapes arranged as fractals, Tanya's second piece is on **professional choices**: orders of magnitude more people google 'how to be a vampire' than 'how to be a mathematician' (there's an important post on the reasons behind that missing, I feel; my good friend **Perpendracula** manages to be both.)

Speaking of my good friends, the Mathematical Ninja was impressed by Pat's brilliant **polynomial** trick and Elizabeth's Ignite talk on the number nine (which looks like a backward P).

Another impressive effort from Michael Croucher (after the deadline, tut tut) showcases all 99 **plot** types in Mathematica, while **Peter picked a peck of pickled podcasts** and suggests that the combination of coughing and enthusiasm in Wrong But Useful - a clear homage to Maths/Maths - was 'awkward'. Meanie!

And that's almost it! Just two more **polished professorial pieces**: The **Pigeonhole Principle** by Jon Kleinberg, and Samuel Arbesman's Wired article on Almost Integers.

Thanks to contributors Dan McQuillan, Patrick Honner, Pat Ballew, Jason Dyer, Richard Mankiewicz, Michael Croucher and the Aperiodical team!

* You can find links to previous editions of the Carnival of Mathematics - or submit your favourite maths posts of the moment - at the Aperiodical's Carnival page.

* Edited 2016-09-11 to fix a broken link

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## peterrowlett

Today is 1st since 30/6/1987 where the date doesn’t contain a repeated digit. Via @icecolbeveridge’s @CarnivalofMath http://t.co/emR82wjfrN

## astrotour2010

RT @peterrowlett: Today is 1st since 30/6/1987 where the date doesn’t contain a repeated digit. Via @icecolbeveridge’s @CarnivalofMath h …

## RealityMinus3

Today is 012345 😀 Courtesy @icecolbeveridge http://t.co/1P5cbeDTmP

## icecolbeveridge

RT @peterrowlett: Today is 1st since 30/6/1987 where the date doesn’t contain a repeated digit. Via @icecolbeveridge’s @CarnivalofMath h …

## niallct

@peterrowlett @icecolbeveridge @CarnivalOfMath Not in ISO with leading zeros. I think that’s 2345-06-17.

## revdal

RT @peterrowlett: Today is 1st since 30/6/1987 where the date doesn’t contain a repeated digit. Via @icecolbeveridge’s @CarnivalofMath h …

## peterrowlett

@niallct @icecolbeveridge you’re right of course, yes. Though 5/4/2013 is not a very contrived way to write it, unlike some similar ‘facts’.

## niallct

@peterrowlett @icecolbeveridge http://t.co/OPlniEwcds . Ruins quite a few ‘patterned’ dates, sadly.

## revdal

http://t.co/yTHOHwWN65 – this is great! I will leave it to you all to find out why…. clue, it’s all about maths and is interesting!

## peterrowlett

@niallct I’m aware of the standard, use it at times, etc. I meant it’s not like @icecolbeveridge’s format is wacky & made up for the trick.

## elliedepends

## Richard Mankiewicz

Hi Colin

Good to see some humour mixed in with the maths.

Have done a bit of social climbing for this page:-) Stumbled too.

## Colin

Thanks, Richard!

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## walkingrandomly

The 97th carnival of mathematics http://t.co/a2Bvr3skx4

## karenlaneuk

This is great…Maths can be fun! http://t.co/6bx4FneSoZ

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