A fact from Distinguishing coloring appeared on Wikipedia's Main Page in the Did you know column on 19 August 2015 (check views). The text of the entry was as follows:
Did you know... that six or more keys on a keyring can be distinguished from each other by coloring the keys using only two colors, but rings of fewer keys require more colors?
This article is within the scope of WikiProject Mathematics, a collaborative effort to improve the coverage of mathematics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.MathematicsWikipedia:WikiProject MathematicsTemplate:WikiProject Mathematicsmathematics articles
Can someone please dumb this article down a bit? For example: In the photograph that accompanies this article, how does one distinguish the three red keys from each other? Maybe I don't understand what "distinguish" means in this context? --Keeves (talk) 16:54, 19 August 2015 (UTC)[reply]
For the keys it is not just the colour, but also the position on the keyring relative to the other keys. Key 1 is red and next to one plain key on one side and two on the other (because it is a closed loop, Key 6 is on the other side of Key 1); Key 2 is plain and next to a red key on both sides; Key 3 is red and next to one plain key and one red key; Key 4 is red and next to one red key on one side and two plain keys on the other, etc. Any key you pick is in a unique sequence of coloured keys. (Brought to you by Belle's Brilliant Brain: getting maths wrong since 19+80) Belle (talk) 17:28, 19 August 2015 (UTC)[reply]
I added the sentence "With such a coloring, each key will be uniquely identified by the sequence of colors surrounding it." Does that help? —David Eppstein (talk) 17:40, 19 August 2015 (UTC)[reply]