Betas 7 and 8 of nauty 2.0 (available approximately Feb 23 to May 26,
2000) contained a bug.

We do not know of any example where nauty gave the wrong answer
without crashing, but the possibility cannot be eliminated.

The error was hard to provoke.  If you did any of the following,
you did NOT encounter the error.

1. Used nauty for a single graph.

2. Used nauty on a sequence of graphs with the same, or increasing,
   or decreasing, or increasing then decreasing, values of 'm'.
   (The only problem case is decreasing then increasing.)
   m is the number of words needed to hold n bits, either
   ceiling(n/32) or ceiling(n/64) depending on your word size.

   In particular, if you only used nauty on graphs of 32 or fewer
   vertices, there was no problem.

3. Used only geng.

4. Used nauty with explicit MAXN > 0 defined.  (The default is MAXN=0.)
   The versions nauty1 and nautyL1 were ok for this reason.

In other cases you might have encountered the bug.  Beta 9 corrects
the bug and has no known problems.  If in doubt, please consult me.

Brendan McKay
bdm@cs.anu.edu.au
May 28, 2000.