[next] [prev] [up] Date: Fri, 05 Dec 80 18:48:00 -0500 (EST)
[next] [prev] [up] From: David C. Plummer <Plummer.SIPBADMIN@MIT-Multics >
[next] ~~~ [up] Subject: That 28 move Plummer Cross

Something I noticed about that 28 move algorithm to get to the Plummer
Cross. Any twist can be the first one made to take the Cross back to
home. The last instructions are (UU DD) which can obviously be (UU D'D'),
(DD UU), and (DD U'U'), so possible backward applications of the
algorithm can start with U,D,U',D'. Add in the three way rotation
symmetry of the cross and you can get all 12 moves as viable first
moves. So, any move takes you closer to home (by this algorithm), so it
has the chance of being the most distant from home. This requirement
(any moves takes you closer) was mentioned by ALAN some time ago. (I
don't hold that the Plummer Cross is the most distant.)

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