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Centers Hinge while the ends U-Turn Back.

\sdform{\boy1n,\girl1s,\girl2n,\boy2s\cr} \sdform{\sboy1s,\girl2w,\sboy2n\cr\spot..,\girl1e,\spot..\cr}
1 1 2 2 1 2 1 2
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\sxvlines{b1s,g2s,b2s,g1s} \systees{g3s,b1n,b4e,g2w}
1 3 2 4 2 4 1 3 3 1 1 3 4 2 2 4
before You All after


This is supposed to be a 4-person call (notwithstanding the immediately preceding diagram), so, when done from a tidal wave, the "centers" are the centers of each side.