Extended hydrogen bonding network predicted (PM5) to be formed by (hexameric) cyameluric acid; the structure would repeat infinitely with 3-fold symmetry. I suggest the centre could be filled by e.g. a guanidinium cation, which can form hydrogen bonds to the six oxygen atoms. The crystal structure of cyameluric acid itself remains unreported! A diagram for cyameluric monoazide was left on Pauling's chalkboard when he died, labelled "Pauling's mystery" and is now preserved for posterity in a museum. An explanation for Pauling's interest has been mooted.