X-Cross: Solve the Cross and First F2L Pair Together

What is an X-cross?

In normal CFOP, you solve the cross first, then put together four F2L pairs (each pair is a white corner and a middle-layer edge). An X-cross combines the cross and the first pair into one step, planned ahead during inspection.

If you follow EasyRubic's layer-by-layer guide, an X-cross is step 1 "White cross" plus one corner from step 2 and one edge from step 3, all done at once. The picture below is step 1 of the guide, the part the X-cross builds on:

According to the SpeedSolving Wiki, the idea of building a small block together with the cross goes back to the 1980s, and Chris Hardwick proposed the X-cross as its own step in July 2003 (SpeedSolving Wiki). Solving two pairs with the cross is called an XX-cross, and it is very rare.

The benefit is clear: you start F2L with three pairs instead of four. The cost is harder inspection, because you have to track two extra pieces on top of the four white edges.

When should you start using the X-cross?

J Perm puts the X-cross among the techniques for solvers under 20 seconds (J Perm). If you are still above 30 seconds, a tidy cross in about 8 moves and smooth F2L will help you much more.

J Perm also says you shouldn't force an X-cross on every solve. Many scrambles are just as fast if you solve the cross and then pair up separately. Treat the X-cross as an option: use it when it's easy to see, and solve a normal cross when it isn't.

At a WCA competition, you get under 15 seconds of inspection before the timer starts (WCA Regulations). The goal of the X-cross is to find the whole solution within that time.

How to hold the cube and read the pictures

Just like in the cross post, hold the cube this way for the whole post:

• White face on the bottom, yellow face on top.
• Green face in front, orange on the right, red on the left, blue at the back.
• The F2L pair solved together with the cross is the front-right pair: the white, green and orange corner and the green and orange edge.

Each picture has two cubes. The cube on the left is the state you have now, with only the centres, the four white edges and the two pieces of the F2L pair coloured in. The cube on the right is the result, flipped so the white face is on top so you can see the cross. When you solve for real, you don't need to flip the cube. The picture in the colour neutral section is different: it colours the four blue edges, and the cube on the right is turned so the blue face is on top.

If you aren't familiar with the R, L, U, D, F, B notation yet, see Rubik's Cube notation for beginners.

How to find an X-cross during inspection

There are no algorithms for the X-cross. The SpeedSolving Wiki lists the number of algorithms for this step as 0: everything is done by intuition (SpeedSolving Wiki). This order of thinking helps you get started:

1. Find the cross first. Plan the cross as usual, ideally in about 8 moves.
2. Guess which piece of the pair will "come along". J Perm's tip: while planning the cross, watch whether an F2L corner or edge will happen to land in the right place after the cross (J Perm). If one does, you only have to worry about the other piece.
3. Adjust the cross solution for the other piece. Usually you only need to change one or two moves, for example turning U at a different moment, so the other piece lands in place too.
4. Can't find one? Let it go. Solve a normal cross, and use the rest of your time to plan the first F2L pair.

The two ideas below make step 3 much easier.

Use the pair's empty slot

While the front-right pair isn't solved, its spot (the front-right corner on the bottom layer and the front-right edge in the middle layer) is an empty slot. An R or F move that passes through that empty slot doesn't break anything. You can move a white edge through it, or park one piece of the pair there for a while.

The idea of using an unsolved slot as a "keyhole" to bring other pieces in is called keyhole (SpeedSolving Wiki). Using keyhole in F2L has its own examples and pictures in the post Advanced F2L tips. For the X-cross, just remember: the more empty slots you have, the more freely you can turn.

The picture below is taken from the worked example further down, with two moves left. The white and red edge sits right in the front-right pair's slot, its white sticker facing the front, while the pair's corner is somewhere else. The move R' brings the white and red edge down to the bottom face through that empty slot, and at the same time puts the green and orange edge in the right way round. The move D2 then finishes everything.

1. You start with (input)
3. After the formula

The opposite is also true: once the pair is in its slot, every R and F move pulls it out again. That's why solvers usually put the pair in last, or bring it in with the very last D move of the cross, as in the worked example below.

The last D turn: the pair comes along

The cross post covered the most important idea: the white edges only need to be in the right order relative to each other, and the last D move brings them all home. The white corner also sits on the bottom layer, so it moves along with that D turn.

So if the white, green and orange corner is in the right position relative to the white edges, and the green and orange edge is already in the front-right slot of the middle layer (where a D move doesn't touch it), then one last D move solves the cross and the pair at the same time.

The picture below is the worked example with only the move D2 left. The four white edges and the white, green and orange corner are all half a turn off, but in the right order relative to each other. The green and orange edge is already in its place in the middle layer, and the D2 move doesn't touch it.

1. You start with (input)
3. After the formula

Worked example: an X-cross in 6 moves

Hold the cube with white on the bottom and green in front, then do this scramble:

B F2 L2 F D L' U' F' D' B2 R2 U2 F

Now the pieces you need are here:

• White and green: top layer, at the back edge, white sticker facing up.
• White and orange: top layer, at the left edge, white sticker facing up.
• White and blue: middle layer, at the back-left edge, white sticker facing left.
• White and red: bottom layer, under the front face, flipped (white sticker facing the front).
• White, green and orange corner: top layer, at the back-right corner, white sticker facing up.
• Green and orange edge: in the right spot at the front-right edge, but flipped.

1. You start with (input)
3. After the formula

The solution L2 F' B2 U' R' D2, move by move:

1. L2: the white and orange edge goes down to the bottom face, under the left face. At the same time, the white and blue edge moves to the front-left edge, its white sticker still facing left.
2. F': the white and blue edge goes down to the bottom face, under the front face. The same move brings the flipped white and red edge up to the front-right edge with its white sticker facing the front, and pushes the green and orange edge up to the top layer. The F' move passes through the front-right pair's empty slot, so nothing is lost.
3. B2: the white and green edge goes down under the back face. At the same time, the white, green and orange corner goes down to the back-left corner of the bottom layer, white sticker facing down.
4. U': brings the green and orange edge above the right face.
5. R': the white and red edge goes down under the right face, white sticker facing down. The green and orange edge also drops into the front-right edge, this time the right way round. This is another move through the empty slot: the pair's corner is somewhere else.
6. D2: the whole bottom face turns half a turn. The four white edges and the white, green and orange corner were already in the right order relative to each other, so they all land in place together. The green and orange edge stays put in the middle layer and matches up with the corner. X-cross done.

We had a computer search every solution on the simulator for this scramble:

• The shortest cross on its own is 5 moves.
• If you solve a 5-move cross and only then pair up the front-right pair, the fastest way still costs 5 more moves, 10 in total.
• The shortest X-cross is 6 moves, like the solution above.

In other words, for just one move more than the cross, you save 4 moves compared with doing each step separately.

Try it yourself: an X-cross for zero extra moves

Hold the cube the same way and do this scramble:

D' L2 D B2 F D B R' B2 L B2 R' U

This time, go for the back-right pair: the white, blue and orange corner and the blue and orange edge. The shortest cross for this scramble is 6 moves. Try to find the X-cross before you read on.

One solution is B2 D2 L F D B': also 6 moves, which means the back-right pair comes along with the cross for zero extra moves. Watch the last move B': it brings the white and blue edge down into place and brings the whole back-right pair home at the same time. The simulator confirms there is no X-cross shorter than 6 moves for this pair.

1. You start with (input)
3. After the formula

What is colour neutral?

Colour neutral means being able to start a solve with a cross of any colour, not just white. The SpeedSolving Wiki splits it into two levels (SpeedSolving Wiki):

• Dual color neutral: you can solve with one pair of opposite colours, for example white or yellow on the bottom.
• Full color neutral: you can solve with all six colours.

The reason is simple: the more colours you can choose from, the more likely you are to get a short cross or an easy X-cross. The SpeedSolving Wiki gives the average number of moves in the shortest cross solution (SpeedSolving Wiki):

• Using one colour only: 5.81 moves.
• Choosing between two opposite colours: 5.39 moves.
• Choosing from all six colours: 4.81 moves.

Try it with the practice scramble above. The simulator says the shortest white cross is 6 moves, and the yellow cross is 6 too, but the blue cross needs just 3 moves. Keep the same grip (white on the bottom, green in front), do U B U, and a blue cross appears on the back face. A solver who only uses white would miss this easy cross.

In the picture below, the cube on the left is the practice scramble you just did, with only the four blue edges coloured in. The cube on the right is turned so the blue face is on top, so you can see the cross. When you solve for real, you would turn the blue face to the bottom and then do F2L as usual.

1. You start with (input)
3. After the formula

Should you practise colour neutral?

Colour neutral has its price. The SpeedSolving Wiki notes that when CFOP became popular in the late 1990s, most top solvers stuck to one fixed colour, because knowing one colour well helps you look ahead in F2L. From around 2008 to 2009, the results of Rowe Hessler and then Feliks Zemdegs brought colour neutral back into the spotlight (SpeedSolving Wiki).

One piece of advice on that page that many people agree with: the easiest way to become colour neutral is to practise it from the very start. Switching colours after thousands of solves with white is much harder.

Practical tips if you are getting started with CFOP:

• New to CFOP: practise both white and yellow right away (dual). You only need to get used to one more colour, but you get an extra option on every solve.
• Used to white for years: no need to switch in a hurry. Spend a few solves a day on yellow, and only use it in competition once you are as fast as with white.
• Playing the 2x2: according to the SpeedSolving Wiki, on small cubes like the 2x2, colour neutral is almost the standard.

X-cross practice drills

1. Unlimited inspection. Scramble the cube, find the whole X-cross before turning anything, then do it without looking again. This is also how J Perm suggests practising planning the first pair (J Perm).
2. For each scramble, try all four pairs. With the same scramble, find an X-cross for each pair (front-right, front-left, back-right, back-left). Often one pair is much easier than the rest.
3. Write it down and count moves. Compare the X-cross with the cross plus a separate pair. If the X-cross is only one or two moves longer than the cross, you have found a good solution.
4. Time your inspection. Once you get it right regularly, use the 3x3 timer and slowly cut your inspection time down to 15 seconds.
5. Add yellow. Each session, do a few solves with yellow on the bottom to slowly become dual color neutral.

Common mistakes

• Forcing an X-cross on every solve. If inspection is almost over and you still don't see one, solve a normal cross. An X-cross that is too long can be slower than solving the cross and then pairing up separately.
• Putting the pair in too early. Once the pair is in its slot, the next R and F moves pull it out. Keep the slot empty as long as you can.
• Forgetting that D moves the corner too. The pair's corner sits on the bottom layer, so it turns along with the white edges. The pair's edge in the middle layer does not.
• Doing one wrong move. You planned the solution, but one wrong turn of the hand ruins the whole plan. Practise slow and accurate before going fast.

Next steps

After the X-cross, you have three F2L pairs left. The post What is CFOP has the overall roadmap, and the next post in the CFOP series covers intuitive F2L: pairing up pieces without memorising algorithms.

With the EasyRubic app, you can scan your real cube with the camera and see the solution step by step on a 3D cube. Download EasyRubic and try finding an X-cross for your next scramble.

Video

Want to see it in motion? The short video below from the JIAYANG channel on YouTube shows more of what this post covers. The video belongs to that channel and is embedded directly from YouTube.

Sources

• XCross (SpeedSolving.com Wiki)
• Cross (SpeedSolving.com Wiki)
• Color neutrality (SpeedSolving.com Wiki)
• Keyhole F2L (SpeedSolving.com Wiki)
• Advanced Cross – J Perm
• WCA Regulations