PLL recognition: all 21 cases from two sides

At PLL the top face is all yellow: everything is read on the sides of the top layer, twelve stickers, of which you only need to see six or eight. Three kinds of clue are enough, and a good cuber recognises any PLL by looking at two sides, without turning the cube.

The three clues

Each side of the top layer has three stickers: corner, edge, corner.

• Headlights: the two corners of a side are the same colour (the edge between them isn’t). Like a car’s two headlights.
• A bar: all three stickers on a side are the same colour. That side is solved.
• A block: a corner and the edge next to it are the same colour, but the other corner isn’t. A block of two.

And remember: you compare the stickers with each other, never with the centre below. The layer can be offset; it doesn’t change any of these clues.

Headlights at the back (Aa)Bar on the left (F)Blocks front and back (T)

First clue: how many sides have headlights?

Corners are the easiest to see. Count the sides that have headlights (a bar counts as headlights).

Sides with headlights	What it means	Possible cases
Four	the corners are placed, only the edges move	Ua, Ub, H, Z
One	two adjacent corners are swapped	Aa, Ab, T, Ja, Jb, F, Ra, Rb, Ga, Gb, Gc, Gd
None	two diagonal corners are swapped	Y, V, Na, Nb, E

The two sides you can see are almost always enough to decide: if both have headlights, it’s four; if one does and the other doesn’t, it’s one; if neither does, it’s either “none” or the headlights are at the back, and the second clue settles it.

Second clue: bars and blocks

Headlights on all four sides (edges only)

• A bar somewhere: Ua or Ub. Put the bar at the back. Look at the front edge: if it matches the headlights on the right, it’s Ua; on the left, Ub.
• No bar: H or Z. Look at one side: is the edge between the headlights the opposite colour to them (red between two oranges, green between two blues)? That’s H. An adjacent colour? That’s Z.

UaUbHZ

Headlights on one side (adjacent corners swapped)

Put the headlights on the left (the same position as T in 2-look). Then:

• The headlights are a bar (that side is solved): F, Ja or Jb.
  • No block anywhere, everything else scrambled: F.
  • A block of two touches the bar (there are other blocks elsewhere, but this is the one that counts): J. With the bar on the left, the block touching it is at the back for Jb, at the front for Ja. In the app, Jb is held with the bar on the left and Ja with the bar on the right: either way, the block touching the bar is then at the back.
• The headlights aren’t a bar (the edge between them is another colour): T, A, R or G.
  • Two blocks, one at the front and one at the back, both touching the headlights (each at a different corner of the left side): T.
  • Two blocks meeting at the same corner, on the right side: a corner and both its edges are already together. Aa if that corner is at the front right, Ab if it is at the back right.
  • A single block, touching the headlights: Ra if the block is at the front, Rb if it is at the back.
  • A single block, not touching the headlights: a G. This is the group that needs the most care; see below.

FJaJbTAaAbRaRb

No headlights (diagonal corners)

• Four blocks, one on each side: Na or Nb. All the blocks are on the right of their side for Na, on the left for Nb.
• Two blocks: Y or V. The two blocks are on two adjacent sides and meet at the same corner (forming a 2 × 2 angle with that corner) for V; they are on two opposite sides for Y.
• No block, all twelve stickers scrambled, three colours on every side: E.

NaNbVYE

The G perms

The four G perms share the same signature: headlights on one side (no bar) and a single block that doesn’t touch the headlights. To choose between the four, with the headlights on the left:

• The block is at the front: Ga or Gd. For Ga, the block is on the right of the front face (against the front-right corner); for Gd, it is on the right face, at the front end.
• The block is at the back: Gb or Gc. For Gb, the block is on the right face, at the back end; for Gc, it is on the back face, at the right end.

GaGbGcGd

In other words: the four G perms have their block at the front-right corner (Ga, Gd) or the back-right corner (Gb, Gc), and all that’s left is to see whether it spills onto the front or back face, or onto the right face. Set up the four cases one after another on the app’s virtual cube: the difference becomes obvious in two minutes, and it’s the best investment in all of PLL recognition.

Summary table

Headlights	Bar	Blocks	Cases
4	1	–	Ua, Ub
4	0	–	H (opposite edge), Z (adjacent edge)
1	yes	0	F
1	yes	3, 1 of them touching the bar	Ja (front), Jb (back)
1	no	2, touching the headlights	T
1	no	2, meeting at the same corner on the right	Aa (front), Ab (back)
1	no	1, touching the headlights	Ra, Rb
1	no	1, not touching the headlights	Ga, Gb, Gc, Gd
0	–	4	Na, Nb
0	–	2 adjacent	V
0	–	2 opposite	Y
0	–	0	E

This table covers all 21 cases with no exceptions. Print the app’s Formulas sheet and write each PLL’s clue next to it: after a few days, you won’t need the sheet any more.

Practice

• Recognise from two sides. Set up a random PLL, give U a random turn, and look only at the front and right. Name the case. If you can’t without turning the cube, check the table for the clue you’re missing.
• Name it before the algorithm. On every solve, say the PLL’s name (in your head) before you start the algorithm. The day you say it without having to search for it, your recognition is there.
• Predict the AUF. Once you have recognised the case, the colours you saw also tell you how far to turn U at the end. Don’t worry about it at first; later on, it saves you half a second on every solve.