Dear Forum,

This is to announce bugfix number 5 for GAP 4.2. The priority of this fix
is high.

You should not apply this fix to any version of GAP3, nor to any
version of GAP4.1.

This fix corrects:

1) a problem with `RationalClasses', which may lead to `ConjugacyClasses'
giving the wrong result,
2) a problem with `CommutatorSubgroup',
3) a problem with `RightSemigroupCongruenceByGeneratingPairs',
4) a problem with a missing html file (`theindex.htm'),
5) an efficiency problem with `RationalClasses',
6) a problem with compiling a loop, where the loop index is not
used inside the loop,
7) some problems with garbage collection, which could cause
corruption resulting unexpected error messages or a crash,
8) a problem with iostreams.

Errors 1), 2) may cause GAP to produce wrong results.

Error 3) may cause GAP to signal an error.

It is not impossible that error 7) could cause a wrong result to be
produced, but this would be most unlikely.

Because of error 8) GAP could open and close only a limited amount of
iostreams.

Many thanks to:
Stefan Kohl for reporting error 1),
Chris Wetherell for reporting error 2),
Isabel Araujo for reporting and fixing error 3),
Dave Hough and Ulrich Hermisson for reporting error 4),
Peter Mueller for reporting errors 5), 6),
Burkhard Hoefling and Volkmar Felsch for reporting error 7),
Greg Gamble for reporting error 8).

Installing the bugfix.
======================

Load the zoo archive `fix4r2n5.zoo' from the bugfixes web page
http://www-gap.dcs.st-and.ac.uk/~gap/Info4/bugfixes.html
Alternatively you can find this file in the `bugfixes' directory of the
GAP4 ftp distribution.

Unpack the file in the home directory of your GAP distribution (the
directory containing the `lib' and `grp' directories) using `unzoo -x
fix4r2n5.zoo'. `unzoo' may ask you for permissions to overwrite files,
answer this with Y)es or A)ll. This will replace the erroneous files by
fixed versions.

(On a PC or a Mac you will have to copy `unzoo' in the same directory and
enter the argument line after the call to `unzoo'.)
Make sure you have write permissions when applying the fix.

This fix changes the kernel. You have to recompile by calling `make' in the
directory in which you unpacked the fix.

Windows users can find a new binary in the file `wbin4r2n5.zoo' in the
`bugfixes' directory: Extract this archive in the same place as the fix
archive to get a new `gapw95.exe' file.

Macintosh users should download the file 'bin4r2n5-PPC.sit' (for PPC
machines) or 'bin4r2n5-68k.sit' (for 68k machines), from the 'bugfixes'
directory.

If you get one of these precompiled binaries you do not need to get any
precompiled binaries that would have come with earlier fixes (these old
binaries are obsolete now). Similarly, if you cannot find these binaries but
have further, newer, fixes to install check whether new binaries with these
fixes did not make the binaries of this fix obsolete.

You can remove the file `description5' afterwards.

After installing the bugfix you can test whether
the bugfix has been applied correctly by starting GAP from the `gap4r2'
directory and issuing

gap> ReadTest("tst/bugfix.tst");
+ bugfixes test
+ GAP4stones: 835
true

(The output should be like this if the bugfixes have been installed
correctly. The number of GAP4stones may vary according to your system.)

Willem de Graaf, 26-September-00