## Interchanging two faces

Submitted by brac37 on Fri, 11/11/2011 - 12:24.Just a question for fun. Suppose you have a Rubiks cube and you want to interchange two faces? How many stickers need to be moved?

Distinguish between opposite and adjacent faces and between using a screwdriver (for disassembling) or not, so you get four answers.

Next, do not read any further before adding those four answers to obtain a single answer.

## Some 3-color cube results

Submitted by Bruce Norskog on Wed, 11/02/2011 - 22:57.The Rubik's Cube can be simplified by using only 3 colors instead of the usual six colors. Generally, opposite faces would share the same color, and that is the convention I assume here in talking about a 3-color cube.

Kunkle/Cooperman showed that a scrambled cube can always be brought to a position within the squares group within 16 moves. This puts an upper bound for God's number for the 3-color cube at 16. It is also well-known that the cube can be put into the <U,D,L2,R2,F2,B2> group in 12 moves. That puts a lower bound on God's number for the 3-color cube at 12. The superflip equivalent for the 3-color cube requires 14 moves according to an optimal 3-color cube solver program I have written. (From solving a million random positions, it appears that about 1.4% of positions of the 3-color cube require 14 moves to solve.) This raises the lower bound for the 3-color cube to 14.

## Source Code for Face Turn Metric 20 Proof Released

Submitted by rokicki on Tue, 10/11/2011 - 12:03.http://cube20.org/src/

I spent a fair amount of effort documenting it. Any feedback is

welcomed.

## 5x5 can be solved in 109 MTM

Submitted by stannic on Mon, 08/15/2011 - 10:53.Any instance of the Twenty-Four puzzle (5x5) can be solved in 109m (multi-tile moves) or less. My proof consists of several steps. It is possible that there is logical error in this proof, so please check it thoroughly. However, I cannot find errors.

## Clarification on how to contact the admin

Submitted by cubex on Sat, 08/13/2011 - 01:51.I've added a link to Martin's indexed cube lovers archive. Also searches for non-authenticated users will now work.

## Approximation formula for the lower bounds of nxnxn cube in slice turn metric

Submitted by kociemba on Wed, 08/03/2011 - 17:40.## Twenty-Four puzzle, some observations

Submitted by stannic on Sun, 07/24/2011 - 01:39.Hello all. I am new on this great forum. My first post is about Twenty-Four puzzle, larger version of classic Fifteen. I walked around sliding tile puzzles for quite some time. At some point I decided that what I have is too much for me alone, but enough to write about it here.

Many small puzzles have been solved long ago. There is some information in OEIS: A151944 (about MxN puzzles), A087725 (about NxN puzzle). AFAIK largest solved STP is 4x4 puzzle (classic Fifteen). It was known that 80 single-tile moves required and sufficient, and recently Bruce Norskog wrote on this forum about 43 multi-tile moves.

## Optimal Void Cube Up Face Odd Parity Maneuvers

Submitted by B MacKenzie on Wed, 07/20/2011 - 13:20.When solving the void cube one encounters odd position parity positions as the cube approaches being solved. The last step for me is to solve the Up face corners and this is where I encounter odd permutations. Corners first solvers may encounter an odd permutation of the Up face edges. The question is what is the shortest maneuver which will convert an odd permutation of the Up face corners into an even permutation of the Up face corners leaving everything else unchanged. This is regardless of the effect on the corner twist. Likewise, what is the shortest maneuver which will convert an odd parity up face edge permutation to an even parity permutation regardless of the edge flip?

## Lower Bounds for n x n x n Rubik's Cubes (through n=20) in Six Metrics

Submitted by rokicki on Mon, 07/18/2011 - 22:12.technique to compute a lower bound on God's Number. This technique

considered the maximum number of positions that can be reached by what

is called "syllables"---consecutive moves on the same axis, possibly

turning distinct faces. Since all the moves that make up a syllable

commute, we can select a single canonical move sequence to represent

every syllable, and then determine how many move sequences of a given

total length can be made out of only these syllables. This gives a

more accurate bound on God's Number because it eliminates many

## Number of 4x4x4 positions for up to 5 moves

Submitted by Bruce Norskog on Sun, 07/10/2011 - 20:35.After hearing about this paper which talks about the size of God's number for nxnxn cubes, I was thinking about what we currently know about God's algorithm for the 4x4x4 and realized that I couldn't seem to find any partial distance distributions on the 4x4x4 on the web.

So I've run my own analyses to get the number of positions up to 5 moves from the solved state. I have done this for six metrics. First, I have "single-slice" metrics where a move is only allowed to turn a single layer. Second, I have twist metrics where a move is only allowed to twist the cube along one plane. This is sometimes called face-turn metric because a face layer (possibly along with additional adjacent layers) is (are) turned with respect to the rest of the cube. Finally I also used what I termed "block turns" where some block of one or more adjacent layers (not necessarily including a face layer) are turned with respect to the rest of the cube. For each of these, I also considered whether or not a move must be restricted to quarter-turns only.