This takes any 2x4 into a 2x4 oriented the other way. Centers become ends
and ends become centers, all by moving forward, back, or sideways, without
turning.
The ends simply move into the center. The centers move out along the opposite
axis. If your nearby end is coming in from your left or right, move forward
or back, or vice-versa.
\syhlines{b2n,g2s,g3n,b3s}
\sxvlines{g3n,b3s,b4s,g4n}
before Slim Down
after
From back-to-back lines, this is the same as Step and Slide.
Slim down can be done in other formations, as long as each quadrant
has one center and one end that are as if in a 2x4.