# Each pair of smartphones has exactly one Dobble app in common

Card game fans might be familiar with the game of Dobble, in which a set of cards featuring symbols is laid out on the table, and family members tear each other’s hands off/eyes out in order to find the one symbol a given pair of cards has in common. Well, it’s now also available virtually!

As discussed at the MathsJam conference in 2012, the set of 55 cards feature a collection of 57 symbols: 8 of them are printed on each card, but in such a way that any two cards share exactly one symbol in common. Martin Whitworth’s slides from the 2012 conference (PDF) discuss the fact that this is possible using an interesting mathematical structure, based on a finite projective plane – but that Dobble could in fact have as many as 57 cards and still retain this property. He even gives the layout of the two missing cards.

Despite this clearly non-trivial imperfection, the game is still huge fun to play, and includes several variants in which you’re trying to build your own stack of cards, get rid of your cards, give your cards to others, make pairs and so on.

The phone-based version, available on Android for £2.13 and iOS for £1.99, has many other variants including different symbols, different numbers of symbols on each card, and allows up to four players on one device (a device which, presumably, you’re ok with people jabbing with their fingers pretty hard onto when they’re excited about having found a match). Download at your own risk.

• #### Katie Steckles

Publicly engaging mathematician, Manchester MathsJam organiser, hairdo.

### One Response to “Each pair of smartphones has exactly one Dobble app in common”

1. Christian Perfect

I have Some Opinions!

As a game on my phone: I’m not keen on how long it takes to load. The music is nice and jaunty, and certainly hurries you along. The mode where you have opponents on either side and have to swipe between them is pretty awkward to play; maybe it’s easier on a bigger screen.

As a Dobble game: the whole reason that Dobble is mathematically interesting is that it’s difficult to make a physical set of cards with the property that each pair has exactly one symbol in common, while keeping a reasonable number of symbols. When the deck doesn’t really exist, you can just make any old nonsense up. It doesn’t change the experience of the game, but my internal Maths Fun Light goes a bit dim.