I'm just starting out on Heyawake. On this puzzle, I didn't see the next logical move, so I tried the 3 box with LRL and then RLR and I didn't have any luck going down those bifurcations. What am I supposed to see here?

I've given you the first word of a 4-word phrase. You'll find the whole phrase once you solve the puzzle below.

Consider the following tetracube (made from 4 unit cubes): It is easy to pack two of these tetracubes to form a 2x2x2 rectangular block. And from that simple packing it is easy to pack any rectangular block where all three side lengths are positive even integers. But is it possible to pack a r...