# Trick: swapping 2 edges (only) on a 3x3



## rubiksarlen (Jan 3, 2012)

Just a trick, everyone can figure this out. There's an explanation to it. :confused:


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## aronpm (Jan 3, 2012)

If you're asking how it works (that is my assumption because of the :confused: emoticon):



Spoiler



By removing the centre caps you've created a Void Cube, which has a parity case. It's caused by the centres not being in a solvable position. 

Here's an example (keep your caps on):
M' (that's the "parity")
U M' U' M (solve DF) 
U' M U2 M' (solve DB)
M' U M' U M' U2 M U M U M U2 (flip UF+UB)
U' (AUF)

If you ignore centres (which is the case if you have them removed), you have now swapped UB and UL.

Doing a single quarter slice turn has the following effect: 4-cycle of edges and 4-cycle of centres. Because centres are ignored, this leaves a 4-cycle of edges which is not solvable on a regular 3x3x3.


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## brandbest1 (Jan 3, 2012)

that's basically a void cube. Void cubes have a parity where two edges can be swapped and the "invisible" centers are swapped along one axis 90 degrees.


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## rubiksarlen (Jan 3, 2012)

nah i knew the trick already but yeah shouldn't have put that emoticon. but still nice explanation.



brandbest1 said:


> that's basically a void cube. Void cubes have a parity where two edges can be swapped and the "invisible" centers are swapped along one axis 90 degrees.



i don't have a void cube, so i thought this was pretty cool. but i'm sure quite some people who don't own a void cube already knows this.


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## Stefan (Jan 3, 2012)

I don't understand why people keep bringing up centers when talking about a void cube, a cube *without centers*. Parity is caused by a 4-cycle of edges, plain and simple. Absolutely no need to talk about centers that aren't even there.


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## aronpm (Jan 3, 2012)

Stefan said:


> I don't understand why people keep bringing up centers when talking about a void cube, a cube *without centers*. Parity is caused by a 4-cycle of edges, plain and simple. Absolutely no need to talk about centers that aren't even there.


 
Because they are removing and re-applying the centre caps from a 3x3, it's relevant information that "the centres are ignored" or "the centres aren't in a solvable position". When there is an edge parity on this 3x3, the "actual" centre colours are not in a position that is solvable without affecting edges, regardless of the superficial colour put on them by the centre caps.

Of course, if he asked about an actual Void Cube, which doesn't have centres, then mentioning the centres would be irrelevant.


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## Stefan (Jan 3, 2012)

To clarify: I wasn't talking about the video (didn't watch it much) but about the posts saying _"a Void Cube, which has a parity case. It's caused by the centres not being in a solvable position"_ and _"Void cubes have a parity where two edges can be swapped and the "invisible" centers are swapped along one axis 90 degrees"_. The latter being *really* bad because even if you do imagine centers there, "swapped along one axis 90 degrees" is just one of several possibilities.


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## aronpm (Jan 3, 2012)

I do agree that I worded that poorly. I should have said something like "[..] a Void cube, which has a parity case. On a normal 3x3x3, it's caused by [...]".

It's nice to have people on the forum that correct semantic errors. Too many kids like correcting syntactic errors. (that isn't sarcasm)


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## samehsameh (Jan 3, 2012)

youve solved the cross on an adjacent face to what it should be if the centers were in place so youve swapped every edge


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## IanTheCuber (Jan 3, 2012)

We're all correct. Its because you solved the cross on an adjacant face, since it is impossible to cycle the centers in steps of 90 degrees. But you didn't know this, since you didn't know what colors the centers were, because its basically a void cube, with no centers.


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## ben1996123 (Jan 3, 2012)

Just do an M and resolve the edges but not the centers.


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## Cielo (Jan 3, 2012)

A shorter alg:
r2 U' M' U r2 U y' U M U M' U


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## chardison1980 (Jan 3, 2012)

its essentually the VOID CUBE parity,


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