Step-by-Step Two-Sided PLL Recognition Guide

[aquila_zyy]

So, I decided to share my take on PLL recognition. I know there are already plenty of very good and detailed guides on the site and YouTube, but I find most of them simply being lists of cases and/or patterns to memorize, which I think are quite intimidating for beginners who are at this level.

Instead of just organizing another library of cases and patterns, I will try to give a full step-by-step guide to my method of recognizing PLL cases, which is made up of manageable sub-steps to distinguish between similar cases. It also has a simpler two-look version, where one first locate the headlight by looking at only two sides (or check that there isn't one).

All images are generated with Puzzle-Gen by tdecker91. I may make a portable pdf later if there is a demand for it.

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Preliminaries​

You should already know full PLL (21 cases), and can recognize all PLL cases instantly if you can see all four sides. You should also be able to instinctively tell whether two colors are opposite or adjacent to each other (you do not need to be able to distinguish between left- and right-adjacency).

Case 0: Easy cases we shall not consider later
We will skip some very easy cases if they appear with their most prominent features already visible, such as F-perm with its long bar visible, or A-perms, V-perms, and Y-perms with their two bars visible. I will also assume you can recognize H-perm, and Z-perm and can distinguish them from the two U-perms from any side.

There are only two set of cases that are worth mentioning for once. They are: N-perms v.s. J-perms, and Ua v.s. Ub-perm.

N-perms v.s. J-perms
These cases may look similar when you can't see the long bar on J-perms. One way to tell them apart is by looking at the color of the "heads" of the "match sticks" relative to their body. On both sides of the two N-perms, the heads have color opposite to their body, but on J-perms, only one side appears with opposite colored match stick.

Furthermore, the long bar on J-perms is always on the opposite side of the side with the opposite colored match stick (see picture).

Side note: The most popular Jb-perm algorithm fixes the corner piece containing the said match stick head.

Ua-perm v.s. Ub-perm​

If you are still mentally shuffling the edges around to tell the two U-perms apart, don't. Instead, you should look for the unique side with the opposite-colored center, as shown in the image below.

One troublesome case is when you see neither the long bar nor the unique center, such as in the following cases:

In such cases, look for the side with the pattern ABAB, and the unique center is always on the opposite side of it.

Case 1: Headlights are visible
In this guide, we show examples where the feature being discussed resides on the left side, but you should be able to mirror the cases if they appear on the right side.

There are 9 possible cases: T, Ra, Rb, the four horsemen of G-perms, and the two A-perms.

T v.s. Ra v.s. Rb

Rb can be easily eliminated as it has a very distinctive ABABA pattern:

To tell the T-perm and Ra-perm apart, normally we would need to peek at the back side to see if there is another bar adjacent to the headlights. A better way to do it would be to check whether the center eye between the headlights is of an adjacent color (which means Ra) or the opposite color (which means T).

G-perms v.s. A-perms
We memorize the features of the four G-perms first, and A-perms can be thought of as their variations.

Ga-perm has an adjacent-colored center eye with an "ear" that is separated from its headlights. This should be how most people identify this case when they learned full PLL:

Gd-perm has an opposite-colored center eye with a "beauty mark" (see picture) on the other side. If you prefer letters over analogies, memorize it as ABACA, but remembering that B is the opposite color of A is important:

Gb-perm is similar to Gd-perm, but without a beauty mark:

Gc-perm has a very distinctive ABAB pattern, with no ear:

Aa-perm can be thought of as a variation of the Ga-perm or Gc-perm. It is a Ga-perm but with a "connected" ear, or a Gc-perm but with an ear. Or, remember it as ABABCC:

Ab-perm can be thought of as a variation of the Gd-perm. It is a Gd-perm but with adjacent-colored center eye. It is the reason why simply remembering Gd as ABACA is not enough:

Case 1.5: How to quickly locate headlights
If you don't want to learn the rest of the guide for now, you can learn a two-look version of it by knowing the following trick to find headlights by looking at only two sides.

If you don't see headlights on the two side facing you, check whether the left-most and right-most stickers are of the same color. This is called "bookends". If you don't see bookends, then it means that there are no headlights in this PLL and it is an opposite corner swap (so one of E-perm, V-perm, or Y-perm). If you do, check the corner piece pointing towards you and locate the sticker that is of the opposite color to the bookends. The headlights are always to the opposite side of that sticker.

Next we will examine the rest of the cases: A bar at the center, a bar on the side, and nothing (garbage case). Cases with two bars are either already the most prominent feature of that PLL, or already discussed in Case 0.

 

[aquila_zyy]

Case 2: A bar at the center
If you see a bar located at the center four stickers, then there are only five cases. They are either: the four horsemen of G-perms, or the Y-perm.

In this case, use the technique introduced in Case 1.5 to identify the Y-perm first: If there is no bookends (or equivalently, the stickers on spot 1&5/2&6 are the same), then this is a Y-perm.

Then, check the color of the sticker next to the bar on the same side. If it is of an adjacent color, then this is a Ga/Gc-perm. Otherwise, this is an Gb/Gd-perm.

There is a shortcut to identify Ga/Gc-perms. We note that in Y-perm, the sticker adjacent to the bar always has the opposite color, so if you noticed that the sticker has an adjacent color, then this must be a Ga/Gc-perm.

 

[aquila_zyy]

Case 3: A bar on either ends of the sides
There are 8 possible PLL cases for this case: Ra/Rb-perm, T-perm, Aa/Ab-perm, V-perm, and Gb/Gd-perm.

The first step is to check if there is an ABA pattern in the center four stickers. For example, Ra-perm has one but T-perm does not:

There is an ABA pattern
Once you see an ABA pattern, check if the sticker farthest away from the bar is of the same color as the bar. If not, which means there is no bookends, we immediately know this is an opposite corner swap and thus must be a V-perm.

Otherwise, this case must be either Ra/Rb-perm, or Gb/Gd-perm. Here we use the trick in Case 1.5 again to locate the headlights, and the exact case should be obvious after that.

You may also simply check whether the sticker next to the bar is of an adjacent or opposite color.

There isn't an ABA pattern
Then we narrow the possible cases down to T-perm or one of the A-perms (only one of them is possible because we do not see headlights).

The rule for this sub-case is easy: Check whether the colors of the two stickers on the corner are adjacent or opposite to their neighboring edges. If both are opposites, then it is an A-perm (left), otherwise it is a T-perm (right).

 

[aquila_zyy]

Case 4: Garbage case
The final case is the worst one, where there isn't any obvious feature at a glance. Do not panic. Once you learned about the patterns, they are not as bad as you think. There are 8 possible PLL cases: V-perm, Y-perm, E-perm, F-perm, Ga/Gc-perm, and Ra/Rb-perm.

Step 1: Look for an ABA pattern in the center four stickers
We do exactly the same thing as in Case 3. This is very convenient, as we normally cannot predict which case our PLL case will fall into (at least not for a beginner). It will be easier on our brain if we look for the same thing in two of the cases.

If you do not see an ABA pattern:
Then this is the Y-perm. Yep, it is surprising that there is such an easy way to isolate one case from the rest seven.

One can also identify the Y-perm by noticing an ABAB pattern on the outer four stickers.


If you do see an ABA pattern:
Step 2: Check if the ABA pattern can be extended

1. If the ABA pattern can be extended on both sides by one more sticker to form an ABCBA pattern, then this is an E-perm.

Side note: The two most common algorithms for the E-perm put the C of ABCBA on the left/right-hand side (i.e. not the front).

2. If the ABA pattern is actually an ABAB on the center four stickers, then this is either an F-perm, or an V-perm. Look for bookends to distinguish the two cases:

Step 3: If the ABA pattern cannot be extended
Then it is either Ra/Rb or Ga/Gc. I feel like this is the only case where there is no good way to identify the PLL cases other than simply memorizing them. You can use the trick introduced in Case 1.5 to locate the headlights, but I find it to cause more confusion sometimes.

If you absolutely dislike memorization, a two-step way to distinguish the four cases is as follows:
1. If the ABA is to the left side, then it is Ra or Gc; if it is to the right side, then it is Rb or Ga.
2. Check the sticker next to the ABA on the outside. If it is of an adjacent color to A, then this is an R-perm; if it is of an opposite color, then this is a G-perm.

From left to right: Ra, Gc, Rb, Ga.

Addendum
Since E-perm is notorious for its lack of features, my brain tends to actively look for an ABCBA pattern when I get a garbage case. I'm not sure why, but I noticed that I tend to identify the Y-perm by the pattern ABC(!B)A, where !B stands for the opposite color of B.

This concludes the guide. I hope you find it useful. If you have your own secret tricks for recognizing specific PLL cases, please share them below!

 

[Mr.Ducky]

Thank you so much for this method, this can help me alot in recognizing pll cases.