# Message #4064

From: Marc Ringuette <ringuette@solarmirror.com>

Subject: 2x2x2x2: U2 parity

Date: Sat, 14 Jul 2018 10:47:26 -0700

Hi, Andy,

That 8 move U2 parity algorithm is so much better than the 18 move one

that I had come up with, thanks! And it is easy to tweak to maximize

cancellations as below.

Your idea of coming up with a complete list of "PBL plus parity" algs,

to avoid ever inserting an explicit parity step, is pretty fancy. In

lieu of the fancy approach, I think I’ll use this method when I’m trying

to minimize moves:

(1) Solve each subcube to "1 turn away from solved" counting parity of each.

(2) Mentally find the shortest solution to the full puzzle ignoring

parity. It will be a trivial solution of <=4 moves. Count parity of

that solution.

(3) If parity would be off, insert a variant of the parity algorithm

(either R2 F2 R2 U’ R2 F2 R2 U’, or R2 F2 R2 U R2 F2 R2 U, or U’ R2 F2

R2 U’ R2 F2 R2) on one of the subcubes now, cancelling the last move of

the parity algorithm with the first move of the computed solution

whenever possible.

(4) Finish the solution.

Cheers

Marc

On 7/13/2018 8:11 PM, Andy F legomany3448@gmail.com [4D_Cubing] wrote:

> … As for solving the U2 parity …

> (R2 F2 R2 U’)2

>

>

>

> On 7/12/2018 6:51 PM, Marc Ringuette ringuette@solarmirror.com

> <mailto:ringuette@solarmirror.com> [4D_Cubing] wrote:

>> 25 Alg for final U2 on R cube (18 moves) 1m16shttps://youtu.be/K2d01CMqtgw

>>