2-Sided PLL Recognition

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2-Sided PLL Recognition (sometimes called "1-Look PLL") is the task of recognizing a PLL from only two adjacent sides (e.g. F and R). This allows a cuber to determine what moves to do as soon as (s)he reaches PLL, without extra AUF turns or cube rotations.

Why 2-Sided PLL Recognition is Possible

2-Sided PLL Recognition is possible because:

  • There are three visible corners, which are uniquely determined. This also determines the hidden one.
  • There are two visible edges.
  • The two hidden edges could be swapped in two different ways. However, given all the visible information there is only one possible way for a valid PLL. This is due to parity.

Therefore, it is possible to tell exactly where each LL piece is (and which PLL case it is). Unfortunately, this is only "barely possible". Unlike OLL (viewed from 3 sides), very few stickers are redundant. For 2-sided PLL recognition, t is sometimes necessary to look at 5 (out of 6) stickers carefully, because changing any one of them could create another valid case.

Existing Systems

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