~~~ From:

~~~ ~~~ Subject:

Responding to Rubin Shai has made me think of an idea which may have

been discussed already.

I was wondering if one could reduce the storage required to represent

a position or pattern. In my notation, one basically records the movement

of each facelet. However, if UR -> RB and we know that the UR piece is moving

to the RB place, then we only need to record the U -> R part of the motion.

In order to know which piece is moving, number all the 54 facelets. Suppose

the facelets of UR are 1,2 in order, and the facelets of RB are 11,12 in order.

Then recording that 1 -> 11 completely describes the movement UR -> RB.

So we only need to record the movement of one of the facelets of

each piece - the others have to follow. Hence we can describe the position

of the cube by a vector of 20 numbers in the range 1 .. 54.

Of course, one has to pay for this - the composition of movements will

be more complex. But if storage is your problem rather than time, it may be

worth it.

DAVID SINGMASTER, Professor of Mathematics and Metagrobologist

School of Computing, Information Systems and Mathematics

Southbank University, London, SE1 0AA, UK.

Tel: 0171-815 7411; fax: 0171-815 7499;

email: zingmast or David.Singmaster @vax.sbu.ac.uk