Unusual Uses of 4x4 Matrices - Phillips & Gunn, 1991

Here's a copy of the paper, "Unusual Uses of 4x4 Matrices," by Mark Phillips and Charlie Gunn, from the Geometry Center, 1991. (This should also be on the Geometry Center web site http://geom.math.uiuc.edu but the link to it isn't working at the moment (9/2016).)