[Cross] Pair the Line

Centers U-Turn Back while the ends Fold.

On a Cross Pair the Line, the centers Trade while ends Cross Fold.

The Fold makes this a semi-space-invader. Breathing takes place laterally (relative to the Fold), but not front-to-back.

\sxhlines{g3s,b1n,b4s,g2n}	\sxvBBBs{...,g2s,b1s,b4n,g3n,...}

before Pair the Line	after

\sxhlines{b2s,g1e,g2w,b1s}	\sxvBBBs{...,...,g1w,g2e,b2n,b1n}

before Pair the Line	after

\syhlines{b2n,g2s,g3n,b3s}	\syvBBBs{b2s,...,g2n,g3s,...,b3n}

before Cross Pair the Line	after