# Good and Bad Edges



## Ninja Storm (Oct 8, 2013)

I was messing around with the cube in Physics yesterday when I came across something that I couldn't really explain to myself.

If the cross is done, why do edges in the E-layer, that are supposed to be there, stay good or bad(using ZZ definition) when doing y or y' rotations?


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## sneaklyfox (Oct 8, 2013)

Two negatives make a positive. In other words, let's say you have white/yellow as your top/bottom colours. If an edge piece does not have one of those colours then it will stay good or bad. So let's say you have the green/red edge between the green/red centers in either orientation (flipped or not)... it will stay good or bad however you look at it, whichever of those colours is part of your EOline. But actually, if you have white/yellow in any of the E layer edges then it WILL flip from good to bad or vice versa. Did that answer your question?


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## whauk (Oct 8, 2013)

they don't!?
setup R U R'. FR is good but if you do a y it (FL) becomes bad.


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## Ninja Storm (Oct 8, 2013)

sneaklyfox said:


> Two negatives make a positive. In other words, let's say you have white/yellow as your top/bottom colours. If an edge piece does not have one of those colours then it will stay good or bad. So let's say you have the green/red edge between the green/red centers in either orientation (flipped or not)... it will stay good or bad however you look at it, whichever of those colours is part of your EOline. But actually, if you have white/yellow in any of the E layer edges then it WILL flip from good to bad or vice versa. Did that answer your question?



I understand that it happens, but I don't understand _why_ this happens.



whauk said:


> they don't!?
> setup R U R'. FR is good but if you do a y it (FL) becomes bad.



I was talking about edges that are supposed to be in the E-layer, sorry for the confusion.


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## Kirjava (Oct 8, 2013)

Edges will not change as long as they are in their correct orbits and vice versa.

For <R,L,U,D,F2,B2> and y rotations, the orbits are U+D edges and E edges.


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## sneaklyfox (Oct 8, 2013)

Ninja Storm said:


> I understand that it happens, but I don't understand _why_ this happens.



Sorry, but I don't get what there is to not understand. Good edges become bad edges and vice versa if there is a flip, right? So when you rotation the cube, there are TWO flips... your orientation flips and the edge piece flips so it stays bad if it's bad and stays good if it's good. Does that explain it?

Edit: Maybe Kirjava's explanation is what you're looking for...


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## Ninja Storm (Oct 8, 2013)

Kir's explanation was what I was looking for, thanks y'all


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## Kirjava (Oct 8, 2013)

Understanding this actually gives you a fast way to check bad edges from other orientations. CN ZZ isn't looking so bad now.


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