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Skewb Blind Discussion (not for Andrew Kang)

Apr 23, 2010
Scotland, UK
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Ok, after this being an obvious thing to do after listening to Cubecast, and being mentioned in episode 7 (which I'm listening to while writing this :)), I felt like making a thread to discuss this. I have solved skewb BLD a few times now (the first time I limited myself to algs that were comms for a laugh), so I can get the ball rolling with my method, and other people can add their ideas (especially people known for BLD solving).

Notation: URF = turn URF corner clockwise, URF' = turn ccw. Easy.

First, it is worth mentioning that there is parity here, and it is annoying to fix. There are two cases, either it can all be solved normally with algs, or a single twist is needed at the start of the solve. There are two orbits of corners on a skewb, which cannot be interchanged. The orientation of each is tied to the permutation of the other, so look at the orientation of each orbit (same as on 3x3x3: UD colours on UD are 0, cw is 1, ccw is -1). If they are both 0 mod 3 everything is fine. If one is 1 mod 3 and the other is 2 mod 3 then a rotation (x or z) will fix it. Otherwise, make the orientation of one 0 mod 3, and a single twist will be needed to fix the other orbit at the start of execution (and tracing pieces will be needed before memoing).

After you either figure out that you don't have parity, or which twist you are going to make to fix parity, time to memo. If a parity fix is needed, trace where the pieces go (and their orientation) and memo them from there. It is possible to permute one orbit of corners at the start with a cube rotation (z2 and/or y). The other orbit will either be solved, or two 2-cycles will be needed. Memo which situation you have.

Then look at which corners you have to flip and in which direction, bearing in mind that when you flip two corners during execution it will be in the same orbit. There are not many corners so this is easy, I just remember what corners need flipped where.

Next is centers. Only 6 of these, so not much to do. I label them A-F and memo about 4 letters for the cycles. Overall, memo is easy since there isn't much there to memo.

For execution, I use a total of 4 algs (sort of 3).

Switch (UFL, URB) (DRL, DLB): z (URB UFL URB' URL')*3 z' (preserves orientation)

Flip (DRF ccw) (DLB cw): (DRF' DRB DRF DRB')*2 (DLF' DRF DLF DRF')*2
(half of this can be used to flip 4 corners in D)

3-cycle centers (F->B->D->F): (DLF' DRF DLF DRF' y2)*2

Any questions, comments, improvements, or mistakes you have spotted are welcome :D. Back to Cubecast ...