Two-colored tiling(s) by science writer Barry Cipra presented at
This Pc'4 tiling has also appeared in page 286 of the October 1999 issue
of the Mathematics Magazine. Rotate each square in every other SW-NE diagonal,
including those containing all-black and all-white squares, by 90 degrees
clockwise, and all other squares by 90 degrees counterclockwise, and you
get the Pc'4mm tiling to the left of it; repeat the process rotating each
square in the opposite direction this time, reversing colors in all
clockwise rotated squares, and you get the Pc'4mm tiling on the cover!