T-Perm Algorithm: Recognition, Finger Tricks and Blindfolded

What is the T-perm?

The T-perm is one of the PLL cases, the last step of CFOP, once the whole top face is yellow. According to the SpeedSolving Wiki, the T-perm swaps the left edge with the right edge of the top layer, and at the same time swaps the two corners on the right: the front-right corner and the back-right corner (SpeedSolving Wiki).

A trick for remembering the name: draw arrows on the top face for the pieces that need to swap. The left and right edges join into a horizontal line, and the two right corners make a vertical line at the end of it. Together they look like a T lying on its side.

The picture below shows the T-perm in the standard grip: yellow face on top, green face in front. On the left is the case you have, on the right is the cube after the algorithm.

If you are not yet used to the letters R, U and F, see the post Rubik's cube notation for beginners first.

The T-perm algorithm

R U R' U' R' F R2 U' R' U' R U R' F'

This is the first algorithm the SpeedSolving Wiki lists for the T-perm. The page also gives a few other algorithms, and suggests trying each one to find the one that feels fastest in your hands, because a shorter algorithm is not always a faster one (SpeedSolving Wiki).

14 moves sounds long, but split into three parts it is much easier to remember:

1. R U R' U': this is the sexy move, the four-move sequence you have already done hundreds of times.
2. R' F R2 U' R': pushes the corners into place.
3. U' R U R' F': finishes off and brings the F face back.

Good to know: doing the T-perm twice in a row puts the cube back where it was. If you do a T-perm by mistake, just do it one more time.

How to recognize the T-perm

The main sign of a T-perm is headlights: on one side face, the two corner stickers of the top row are the same colour. A T-perm has headlights on exactly one side, and the edge sticker between the headlights is the opposite colour (red goes with orange, green goes with blue).

The algorithm only works when the headlights are on the left face. So before you start, turn U until the headlights are on the left. The table below covers all four angles:

Each picture below includes the U turn at the start of the algorithm, so you can see that the picture on the right is always a solved cube.

Headlights on the left face

This is the grip for doing the algorithm. The red headlights are on the left face, so you cannot see them. Instead, you see:

• Front face: green, green, orange. The two greens are a pair on the outside.
• Right face: blue, red, green. The two corners are opposite colours.

Headlights on the front face

The front face is red, orange, red: two red headlights with orange in the middle, the opposite colour of red. The right face is green, green, orange: the green pair sits next to the middle corner. Turn U once, then do the T-perm.

Headlights on the right face

The right face is red, orange, red. The front face is orange, blue, blue. Turn U2, then do the T-perm.

Headlights on the back face

Neither face you can see has headlights. The front face is blue, red, green: two corners of opposite colours. The right face is orange, blue, blue: a pair on the outside. The headlights are on the face across from the one with two opposite-coloured corners, which is the back face. Turn U', then do the T-perm.

To recognize all 21 PLL cases from just two faces, see the post PLL recognition.

The T-perm in 2-look PLL

If you are working through 2-look PLL, the T-perm is the corner-swapping algorithm in step 1. In this step you only look at the four corners and ignore the edges:

• One face has headlights: move the headlights to the left and do the T-perm. All four corners will be in the right place.
• It does not matter if the edges get mixed up more, step 2 will fix them.

The picture below only colours the four corners, which is exactly what you need to look at in step 1. The red headlights are on the front face, so the algorithm starts with U.

Finger tricks for the T-perm

Finger tricks mean turning the faces with single fingers instead of your whole hand, so you have to change your grip less often. The SpeedSolving Wiki sorts turns into three kinds: push (bending a finger in), pull (stretching a finger out) and wrist turns for R and L (SpeedSolving Wiki).

Here is one way many people do the T-perm, following the three parts above:

1. R U R' U': R and R' with your right wrist. U is a push with your right index finger, U' a push with your left index finger.
2. R' F R2 U' R': after R', your right index finger is already on the front face, so use it to push F. R2 is two wrist turns in a row. U' with your left index finger.
3. U' R U R' F': U' again with your left index finger, then R U R' as in part 1. For the final F', use whichever finger feels comfortable, as long as you do not have to change your grip.

The part worth paying the most attention to is the U' R' U' in the middle of the algorithm. The SpeedSolving Wiki calls this a "disjointed double flick": a U2 turn gets interrupted by another move, so it is split into two separate U' turns, both with your left index finger. The page uses the T-perm itself as its example (SpeedSolving Wiki).

How to practise: go slowly first so you use the right fingers, then speed up little by little. The SpeedSolving Wiki advises against pushing for speed too early, because bad habits are very hard to break. For more kinds of turns, see the post Rubik's cube finger tricks.

The J Perm video below shows the T-perm in the corner-swapping part of 2-look PLL, and lets you see the hands at real speed:

https://www.youtube.com/watch?v=f_Yor-ydZjs Video: J Perm, Rubik's Cube: Easy 2-Look PLL Tutorial (Beginner CFOP)

The T-perm in blindfolded solving

The T-perm is not just for speed. In Old Pochmann, the simplest blindfolded method, the T-perm is the main algorithm for placing the edges. According to the SpeedSolving Wiki, the method was invented by Stefan Pochmann and solves one piece at a time (SpeedSolving Wiki).

The idea, following the Ruwix guide (Ruwix):

• The edge at top right is the "buffer". The T-perm swaps it with the edge at top left.
• To swap the buffer with an edge somewhere else, do a few setup moves to bring that spot to the top-left position, do the T-perm, then undo the setup moves.
• The setup moves must not touch the buffer or the two right corners.

In the pictures below, only the buffer, the edge being swapped and the two right corners are coloured.

No setup needed: top-left edge

Bottom-left edge: setup L2

Full sequence: L2, T-perm, L2.

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

Front-left edge: setup L'

Full sequence: L', T-perm, L.

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

Back-left edge: setup L

Full sequence: L, T-perm, L'.

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

What about the two swapped corners?

Every T-perm also swaps the two right corners. Doing the T-perm twice puts those corners back, so if the number of edge swaps is even, the corners end up correct by themselves. When the number is odd, Ruwix calls this parity and fixes it with a different PLL algorithm before finishing the edges. That part is beyond this post; you can read about it in the Ruwix guide.

The picture below shows a case solved with two swaps in a row: the bottom-left edge, then the front-left edge. Three edges cycle around, while the two right corners are not swapped, because the two corner swaps cancel each other out.

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

Common mistakes

• Doing it before the headlights are on the left. This is the most common mistake. Always turn U first.
• Mixing up the T-perm with other cases that also have headlights. In a T-perm, the edge sticker between the headlights is the opposite colour. If it is a neighbouring colour (for example red with green), it is a different case.
• Changing your grip in the middle of the algorithm. Getting the finger tricks right from the start saves you fixing them later.

Sources

• PLL (SpeedSolving.com Wiki)
• Finger tricks (SpeedSolving.com Wiki)
• Old Pochmann (SpeedSolving.com Wiki)
• How to Solve the Rubik's Cube Blindfolded (Ruwix)