in diagonal, orient with Y2 to reverse between clock and counterclockwisein diagonal, orient with Y2 to reverse between clock and counterclockwise
opll_butterfly_-+
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L' U' L' U R U' L U R' L |  |
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Memorization: (L' U' L' U) (R U' L) (U R' L)
on the same face, version clock and counterclockwise
counterclockwise
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U' R2 D R' U2 R D' R' U2 R' |  |
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clockwise
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L F R' F' L' F R F' |  |
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Memorization: U' R2 D R' U2 R D' R' U2 R': roughly pattern U R D R x 2, but difficult to find any shortcut or mnemonic hook
Memorization: L F R' F' L' F R F': L R' L' R interwoven with F F' F F'