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From: wpt@princeton.UUCP (William Thurston)
Newsgroups: sci.math
Subject: angels and devils
Message-ID: <2056@princeton.UUCP>
Date: Thu, 16-Oct-86 21:04:49 EDT
Article-I.D.: princeto.2056
Posted: Thu Oct 16 21:04:49 1986
Date-Received: Fri, 17-Oct-86 03:17:31 EDT
Distribution: net
Organization: CS Department, Princeton University
Lines: 14
Keywords: game

John Conway is at Princeton this year, and he has a great stock of
interesting questions.  Here is an unsolved problem:

Imagine a universe consisting of planets arrayed at the grid points
of an infinite plane.  On one of the planets, an angel is sitting.
Every day, the angel can fly off to another planet, but the angel's
range is limited to a distance of (say) 100.

Unfortunately, there is a devil in the universe.  Every day, the devil
can destroy a planet, anywhere in the universe.

Can the angel forever avoid being trapped?

Bill Thurston    ...!princeton!wpt