Talk:Four color theorem

flaw in colors of the map at the top of the four-color theorem article

In the picture at the top of the article, take the orang colored squarish item. to the upper left there is a blue section that is triangle ish shaped that should be yellow as it is now the blue is adjacent at a point to two other blue sections that are spikey. A point counts as they are touching. pls fix. 73.180.167.41 (talk) 12:26, 24 February 2023 (UTC)

Adjacency at a single point does not count as adjacency for the purposes of this theorem. As the article already clearly states: "regions are adjacent if they share a boundary segment; two regions that share only isolated boundary points are not considered adjacent." —David Eppstein (talk) 16:01, 24 February 2023 (UTC)

Use "colour" not "color" when quoting British mathematicians

There are several quotations here from British mathematicians which are not spelled as they would have originally been made, and which I think should be emended for veracity. 92.27.162.236 (talk) 09:41, 16 May 2023 (UTC)

Context: the above comment is an opening to the discuss step of WP:BRD, following my revert Special:Diff/1154889964 and my explanation at the IP editor's talk page User talk:92.27.162.236#A change of 'color' to 'colour' in Four color theorem. --CiaPan (talk) 12:14, 16 May 2023 (UTC)

There is no doubt that British mathematicians used the word "colour" in everything they wrote on the subject, not "color". Just because an American work is used as a source should not imply that the word was spelled "color" by any of the original British authors.

There must be original British sources which should be quoted first hand. "Color" is factually incorrect, and should be changed. 92.27.162.236 (talk) 03:09, 24 May 2023 (UTC)

Indeed, by looking at the facsimile of De Morgan's letter you will be able to read the words "coloured" and "colours" for yourselves. 92.27.162.236 (talk) 03:16, 24 May 2023 (UTC)

We should certainly use the original spelling, regardless of ENGVAR, as we do also for certain quotations using archaic spellings rather than attempting to modernize them. (Not that I think UK spelling is in any way archaic, but I think the precedent is similar.) —David Eppstein (talk) 06:51, 24 May 2023 (UTC)

Re: the recent added images of colorings of different countries

I agree with David Eppstein that adding an entire section as a gallery to simply present different countries with their colorings is a bit overkill (especially with the map of America's at the beginning). I was thinking, though, of re-adding at least one of them to the section "Use outside of mathematics," since it seems apt. I was originally just going to place the Germany one in, but maybe adding a picture of a real-life exclave forcing 5-colors would be nice. In any case, I don't think it hurts to add a second picture illustrating how it works, since non-math inclined people are probably going to be interested in (more than one) examples of these type. I didn't want to just make the edit immediately though since the similar one had just been reverted. What do other people think? _{Integral Python} ^{click here to argue with me} 21:58, 24 May 2023 (UTC)

Equivalence to torus coloring is wrong

The article says "Forcing two separate regions to have the same color can be modelled by adding a 'handle' joining them outside the plane. Such construction makes the problem equivalent to coloring a map on a torus (a surface of genus 1), which requires up to 7 colors for an arbitrary map." That seems to imply that there's a planar map with just one noncontiguous region that requires 7 colors. But you can 4-color the contiguous countries and then use 1 more color for the noncontiguous one, so you only need 5 colors. I don't know how this should be rewritten. Nylimb (talk) 14:41, 23 August 2023 (UTC)