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Step 4 of 6

Edge orientation

What you should end up with

Six edges are left: four on top and two on the bottom in the middle slice. Only M and U moves are needed. First all the edges have to become good: the yellow or white sticker points up or down. Guides call this step 4a, or EO.

How to do it

Do M or M' so the top centre is yellow or white. The rule below only works then.
Look only at the yellow and white stickers of the six edges. A good edge shows such a sticker up or down, a bad one to the side. The corners do not matter here.
You cannot see the bottom back edge, but you can work it out: the number of bad edges is always even. Count the five you can see.
Turn the top to match the diagram and do the formula. In the diagrams the bad edges are purple and the corners grey: they do not get in the way here. The bottom is drawn as if you were looking down through the cube.

The main case: the arrow

Arrow, bad edge at the bottom front Three bad edges on top. Turn the top so the good one is at the back. M' brings all four bad edges to the top, U' fixes them, and the second M' puts a yellow or white centre back on top.

M' U' M'

Arrow, bad edge at the bottom back The same, mirrored. Hold the good top edge at the front.

M U' M

Four bad edges

All four on top None bad on the bottom. The first part of the formula makes an arrow, and the second solves it.

M' U2 M' U2 M' U' M'

Two together on top and two on the bottom Hold the bad top edges at the back and on the left.

M2 U' M' U' M'

Two opposite on top and two on the bottom Hold the bad top edges on the left and right.

M' U2 M' U2 M U M'

Two bad edges

Two together on top Hold them at the back and on the left.

M' U M' U2 M' U' M'

Two opposite on top Hold them at the front and at the back.

M' U' M U M' U' M'

One on top, one at the bottom back Hold the bad top edge at the front.

M' U' M' U' M U' M'

One on top, one at the bottom front Hold the bad top edge at the back.

M U' M U' M' U' M

Both on the bottom All the top edges are good.

M' U' M' U M U' M'

Six bad edges

All six The longest case and the rarest. The first part reduces it to an arrow.

M' U M U2 M U M' U M U' M'

Tips

›Nearly all the formulas end with an arrow. If you forget one, look for a way to reach an arrow with M and U.

›Only a U move with the centres out of position changes orientation. That is why every formula moves the middle slice first.

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