Re: What databases have taught me
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 25 Jun 2006 12:56:29 GMT
Message-ID: <1Kvng.1969$pu3.50958_at_ursa-nb00s0.nbnet.nb.ca>
>
> Doesn't region identification depend on the topology of the space? If your
> graph were on the surface of a torus, wouldn't you come up with possibly
> different regions? (viz. the seven color map theorem for the surface of a
> torus)
Date: Sun, 25 Jun 2006 12:56:29 GMT
Message-ID: <1Kvng.1969$pu3.50958_at_ursa-nb00s0.nbnet.nb.ca>
David Cressey wrote:
> "Chris Smith" <cdsmith_at_twu.net> wrote in message
> news:MPG.1f07b8374b49cf619896f9_at_news.altopia.net...
>
>>2. Identify all of the regions. Regions are the empty spaces on your >>paper, and are separated by edges from the graph. The blank space >>outside of where you've drawn the graph DOES count as a region, so there >>is always at least one. If the graph is a tree, for example, then there >>is only one region, so the dual only has one vertex.
>
> Doesn't region identification depend on the topology of the space? If your
> graph were on the surface of a torus, wouldn't you come up with possibly
> different regions? (viz. the seven color map theorem for the surface of a
> torus)
If it were on a torus, it would not be on a plane.
Damn! Now I have that song going through my head: "I leaving on a jet plane. Don't know when I'll be back again..."
Now you all do too! So there! Received on Sun Jun 25 2006 - 14:56:29 CEST