FOUR

Perfect Clear Opener (パフェクリテンプレ)

A very popular perfect clear opener where you have an 84.64% chance of doing a perfect clear if you have I on hold. Often abbreviated as PCO.

If you are unable to hold your I, your chance of doing a perfect clear decreases to 61.19%


Solutions

Vertical I

The only potentially non-straightforward solution would be the one using IJZS. Rotate CCW CCW CCW.

These solutions are also used in Grace System when you have a vertically placed T.

1st Row I

3rd Row I

Others

2-height PC

There is a slight chance (approximately 2%) to do a 2-height perfect clear after doing your first PC. Example.


Recovery

These are some follow-ups that you could do when a perfect clear is not possible.

Tetris

The simplest way of recovering is to build a Tetris after sliding in an L or J underneath, as shown on the first image. Note the placement of S on the second image.

Kaidan

It is often possible to build a Kaidan when you can't do a perfect clear. You will be able to follow up with a Tetris afterward immediately. Notice how S and Z are placed on the third image.


Compare the placement of S on your stack between when you would build Kaidan (first row) and when you would build a Tetris (second row)


TST

Depending on your next pieces after placing your S like the first image below, you could build a TST instead of a Tetris.


credit to kazu for the example

Unnamed Technique

These are alternate recovery patterns that you can use. Refer to this fumen to see how you can spin in certain pieces while setting these up.

Misc

PCO covers the vast majority of opening bags (92.46%), but you can't build it the standard way with sequences such as SOZITLJ. For those, try stacking the same shape these ways:



You just need the first two. With these patterns, you should be able to open with PCO for every first bag sequence.

See Also / References

Perfect Clears

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