Paul Stephenson

Plato's Fourth Solid and the "Pyritohedron"

Michael Deakin’s article (“A simple proof of the Beijing theorem” 76 pp251-4) will have set readers thoughts running in a number of directions. Mine turned backwards in time, towards rational approximations to the golden ratio and crystallography. The symmetries of the crystal lattice preclude the appearance of a regular pentagonal face or true 5-axis. However fair rational approximations are attained with surprising ease.