Martin Erickson

In "Beautiful Mathematics," pages 106-108, section 5.17, "A Group of Operations," Martin Erickson does not acknowledge any source.

That section, on a group of 322,560 permutations generated by permuting the rows, columns, and quadrants of a 4x4 array, is based on the Cullinane diamond theorem. See that theorem (published in an AMS abstract in 1979) at PlanetMath.org and EncyclopediaOfMath.org, and elsewhere on the Web.

Details of the proof given by Erickson may be found in "Binary Coordinate Systems," a 1984 article on the Web at http://finitegeometry.org/sc/gen/coord.html.… (altro)