The paper contains two figures tetrahedron.ps and
graph.ps which need to be downloaded separately. (If you print the paper with the
figures,they will look better printed at 600dpi.)
There are two proofs of the main theorem given in the paper.
Unfortunately, one of them contains an error, pointed out by Stephan Endrass
and Duco van Straten. A short correction
will appear in J. Alg. Geom.; Fortunately the second proof is correct.