# Is a SuperCube Safe Single Dedge Flip Algorithm Possible in <U, Rw>?



## Christopher Mowla (Jun 14, 2012)

A little while ago, cuBerBruce found the following four (34 qtm, 26 ftm) move solutions with k-solve:
Rw U Rw' U Rw' U' Rw2 U Rw2 U2 Rw' U2 Rw U2 Rw' U2 Rw' U Rw' U' Rw U Rw' U2 Rw U2
Rw' U' Rw U' Rw U Rw2 U' Rw2 U2 Rw U2 Rw' U2 Rw U2 Rw U' Rw U Rw' U' Rw U2 Rw' U2
Rw' U' Rw U' Rw U' Rw2 U2 Rw2 U' Rw U2 Rw' U2 Rw U2 Rw U Rw U Rw' U' Rw U2 Rw' U2 
Rw U Rw' U Rw' U Rw2 U2 Rw2 U Rw' U2 Rw U2 Rw' U2 Rw' U' Rw' U' Rw U Rw' U2 Rw U2

Looking at a 4x4x4 supercube after each is applied, we can see that two X-center pieces in the top layer are swapped, and the right center is rotated 90 degrees. With the move restriction <U, Rw>, one cannot possibly do a 3-cycle of X-center pieces inside the top center and the right center.

This made me question whether or not a supercube safe algorithm for this case (or any other 2-cycle of wings case) in <U, Rw> is even possible.

I tried another route to make an algorithm like this, but similar to my poor approach in <U, Rw> it's very long. You'll definitely need a supercube applet to see that the following is supercube safe. It has a scary length of (1543 qtm, 1152 ftm) and (1527 qtm, 1141 ftm) if you cancel moves with each of the main pieces. Each of the main pieces are repeated. So you can look at what those do separately if you're interested to see how I made this by hand.

(SiGN Notation) [Link]

r' (r2 U2 r U2 r2 U' r' U2 r' U r' U' r U r' U' r U2 r2 U2 r2 U2 r U r U' r' U r U2 r' U' r U r' U' r' U2 r2 U2 r2 U2 r' U r U' r' U r U r U2 r U r2 U2 r' U2 r2 U2 r2 U2 r U2 r2 U' r' U2 r' U' r' U' r U r' U' r U2 r2 U2 r2 U2 r U r U' r' U r U2 r' U' r U r' U' r' U2 r2 U2 r2 U2 r' U r U' r' U r U' r U2 r U r2 U2 r' U2 r2 U2 r U2 r2 U2 r U2 r2 U' r' U2 r' U r' U' r U r' U' r U2 r2 U2 r2 U2 r U r U' r' U r U2 r' U' r U r' U' r' U2 r2 U2 r2 U2 r' U r U' r' U r U r U2 r U r2 U2 r' U2 r2 U2 r2 U2 r U2 r2 U' r' U2 r' U' r' U' r U r' U' r U2 r2 U2 r2 U2 r U r U' r' U r U2 r' U' r U r' U' r' U2 r2 U2 r2 U2 r' U r U' r' U r U' r U2 r U r2 U2 r' U2 r)3 r (r U r U r U' r' U2 r2 U2 r U2 r' U r2 U' r2 U' r U2 r' U' r U2 r' U r U2 r' U' r U2 r' U' r U2 r' U r U2 r' U' r U2 r' U' r U2 r' U r U2 r' U' r U2 r' U' r U2 r' U r U2 r U r2 U' r U2 r2 U2 r2 U2 r' U2 r U2 r' U2 r' U2 r2 U2 r2 U2 r' U2 r2 U r' U' r' U' r' U' r U2 r' U r U2 r' U2 r U r' U r U2 r' U2 r U r' U r U2 r' U2 r U r' U r U2 r' U2 r U' r' U' r U r' U2 r U2 r' U' r U' r' U2 r U2 r' U' r U' r' U2 r U2 r' U' r U2 r' U' r U r' U2 r U2 r' U' r U' r' U2 r U2 r' U' r U' r' U2 r U2 r' U' r U2 r')2 (r U r' U r' U r2 U2 r2 U r' U2 r U2 r' U2 r' U' r' U' r U r' U2 r U2)2 r

The big problem is that it also does the move R.

So the one question we have to answer is if the move R' (on applied on the supercube) can be reached in <U, Rw>.

If it isn't possible to do the move R' on a 4x4x4 supercube with <U, Rw>, then it is definitely impossible for a supercube safe 2-cycle of wings to exist. And if so, is there a way someone could find the optimal solution (with k-solve or whatever program is out there) for my alg? (I would be interested to see how long the optimal solution is for a supercube dedge flip + the move R in <U, Rw>).


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## qqwref (Jun 15, 2012)

Consider an algorithm in <U,Rw> that changes the parity of the wings. Since Rw is the only type of move that can affect parity, there must be an odd number of Rw's (in qtm). But we can also notice that Rw is the only type of move that can affect the right center - and the right center can only be solved if there are an even number of Rw's (in qtm).

So, sorry, but a supercube parity algorithm in <U,Rw> cannot leave the right center solved


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## vcuber13 (Jun 15, 2012)

cmowla said:


> With the move restriction <U, Rw>, one cannot possibly do a 3-cycle of X-center pieces inside the top center and the right center.


why?


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## Noahaha (Jun 15, 2012)

vcuber13 said:


> why?



No matter how many Rws and Us you do you cannot affect the right center.


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## Christopher Mowla (Jun 15, 2012)

qqwref said:


> Consider an algorithm in <U,Rw> that changes the parity of the wings. Since Rw is the only type of move that can affect parity, there must be an odd number of Rw's (in qtm). But we can also notice that Rw is the only type of move that can affect the right center - and the right center can only be solved if there are an even number of Rw's (in qtm).


I can't believe I didn't think about that! Now I still would like to see an optimal algorithm which does the same thing as mine. 

EDIT: This also must mean that you cannot do R or r in <U, Rw>. That's insane!


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## qqwref (Jun 15, 2012)

cmowla said:


> I can't believe I didn't think about that! Now I still would like to see an optimal algorithm which does the same thing as mine.


Mm, yeah. Bruce's ksolve solutions are impressive, a solution of that long must take quite a while to compute...



cmowla said:


> EDIT: This also must mean that you cannot do R or r in <U, Rw>. That's insane!


I dunno, maybe you can, just not supercube-safe. It's possible to do a non-supercube-safe R move by doing your alg followed by U r U r' U r' U' r2 U r2 U2 r' U2 r U2 r' U2 r' U r' U' r U r' U2 r U.


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## Christopher Mowla (Jun 15, 2012)

qqwref said:


> I dunno, maybe you can, just not supercube-safe.


Oops, yeah I meant on the supercube.

But we can do R2 on the supercube:
([[U2 Rw U2 Rw2 U2 Rw' U' Rw' Rw2 U2 Rw2 U2 Rw2 U2 Rw U Rw U2 Rw2 U2 Rw' U2, Rw2], Rw] Rw2)3
and therefore also r2 (if you add Rw2 at the end of that alg).

It would be neat to get the optimal sequence to make r2 and r (on the non-supercube) so that we can write all algs using all wide and outer layer turns (just for fun).


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