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From: ags@pucc-i (Seaman)
Newsgroups: net.ai
Subject: Re: Four color...
Message-ID: <209@pucc-i>
Date: Fri, 17-Feb-84 16:19:17 EST
Article-I.D.: pucc-i.209
Posted: Fri Feb 17 16:19:17 1984
Date-Received: Mon, 20-Feb-84 06:54:37 EST
References: <5540@uiucdcs.UUCP> <1290@mit-eddie.UUCP>
Organization: Purdue University Computing Center
Lines: 17

>  I had thought that 4 color planar had been proved, but that 
>  the "conjectures" of 5 colors for a sphere and 7 for a torus 
>  were still waiting.  (Those numbers are right, aren't they?)

The sphere problem is equivalent to a plane problem.  Just prick a whole
in the middle of one of the regions and flatten it into a plane.  Therefore
4 colors are sufficient for a sphere.

Seven colors were known to be necessary and sufficient on a torus, long
before the four-color proof was found for the planar case.
-- 

Dave Seaman
..!pur-ee!pucc-i:ags

"Against people who give vent to their loquacity 
by extraneous bombastic circumlocution."