Step 4: the Last Layer cross
This is an easy step, which needs only one algorithm
For this cross, you really only need one short algorithm. First, lets look at the four possible situations for the last layer.
- The cross is already there.
- Two opposing edges are flipped
- Two adjacent edges are flipped
- All edges are flipped
The cross is already there
Do nothin'!
moves will appear here
Two adjacent edges are flipped
For both cases, make sure one of the flipped edges is in the front, and the other one is on the left. Then perform this algorithm:
moves will appear here
This one flips the front and left edges.
Two opposing edges are flipped
You will have to perform it twice for the situation where opposing edges are flipped (front and back).
moves will appear here
Alternatively, you can use the reversed algorithm instead of performing the previous algorithm twice. To make a reversed algorithm you read from right to left and invert the moves.
moves will appear here
All edges are flipped
If you think about it, the solution is simple: you have to perform both algorithms. In between you have to reposition the last layer so the next set of edges is flipped.
moves will appear here
Speedcubing Tips
If you're practicing for speed, try to flip the cube before you start, so the last layer is now on top. This makes it easier to use so-called finger tricks, especially for these algorithms. Most speedcubers can perform this algorithm blazing fast, and it's one of my personal favorites as well. For a fast version of the last algorithm you would perform:
moves will appear here
almost as one finger trick, without ever regripping the cube.
I seem to be unable to apply that algorithm so as to actually make it work. Applying it over 2 adjacent corners will also flip the other 2. I can’t trust this solution.