[rytpeamw] Partial face turning

Twisty puzzle (first) in 2 dimensions: Start with an MxN grid of squares.  Select any 2x2 block of squares and rotate them 90 degrees.  Or any square sub-block of any size.

Or, from any internal location, shoot 4 orthogonal rays.  Select the last square on each ray before the ray exits.  Permute and rotate those 4 squares on the "surface" of the MxN rectangle.  This method avoids the moves from being local, making for a more difficult puzzle vaguely in the style of a 2D Rubik's cube.

Easily extendible to 3D: remove a 2x2x2 sub-block, or exploded sub-block, rotate it, and put it back.  Or, manipulate the sub-block like a 2x2 Rubik's "Pocket" cube.

Reflections possible also.