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2-sided PBL recognition guide

Zarxrax

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Jan 7, 2009
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Just a very simple guide for recognizing PBL by looking at only 2 sides. This is very simple, but it took me much longer to figure it out than it probably should have.


1. If you see a "bar" then you have an adjacent swap permutation on that layer, on the pieces opposite the bar.


2. If all pieces on the layer are different colors, then you have a diagonal swap permutation.


3. This is the only situation that can be a bit hard to work out, but if you know the trick to it, its quite simple. If you see the same color on diagonally opposite corners (for example the 2 red faces in the top layer), then you have an adjacent swap. But, just looking at 2 sides, how do you know where the bar is located?
Just look for 2 opposite colors side-by-side. Here we can see the red and the orange beside each other. This tells us that these are the two pieces that need to be swapped. The bar is located opposite from them, on the back layer.


Adjacent swap and diagonal swap are the only permutation cases that can happen on the 2x2x2 cube. PBL solves them for both the top and bottom layers simultaneously.
 

abctoshiro

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Apr 2, 2010
Messages
162
This is how I get it: this, I think, is a 2 part recognition system. First, recognize which case is at the top layer. Then, apply the same rules to recognize the bottom layer. At first, it may take some time, but after some practice, it will be faster to recognize.
This is just how I understand this. If I have a mistake, tell me.
 

CubicNL

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Jan 3, 2011
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2011WILD01
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CubicNL
That's how it is.
But if you use Ortega (this is much harder on guimond) you can easily see the bottom layer case in your inspection, so that you only have to look at the top layer, (auf if needed) and then PBL
 

Zarxrax

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Jan 7, 2009
Messages
1,254
Location
North Carolina
Yep, with practice you should be able to predict the bottom layer every single time with ortega, its pretty easy.
Knowing the bottom layer permutation, I think that means that there are always only 2 possibilities for the PBL, based on which case you get for the top layer.
 
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