In his message of 13 May 1993 Tom McDonough desrcibes

some difficulties encountered in the
use of the CharTable function to get character tables of Weyl groups
of type D.

These problems came into the package with the new concept for strings
in GAP.

The classes and characters of Weyl groups of type D are labelled by
pairs of partitions. For even rank certain labels occur twice. They
are distinguished by a "+" or "-" sign in the place of the second
partition. The functions for the constuction of the character table
try to recognise these signed labels by 'IsString(pi[2])'.

But the second partition may also be empty, represented by the empty
list. And due to the new string concept, the empty list is now
recognised as a string, too. This leads to the problems encountered
by Tom McDonough.

This will be fixed with the next upgrade. Then the signs in the
labels will no longer be strings but single characters: '+' and '-'.
This means 'CharTable("WeylD", <n>)' and 'CharTable("Alternating",
<n>)' will then produce slightly different results. I hope this
causes no problems.

In the meantime a possible workaround is to replace the function
'IsString' by one that ignores the empty list:

gap> IsStr:= IsString;
function (...) internal; end
gap> IsString:= function(obj)
> return obj <> [] and IsStr(obj); end;
function ( obj ) ... end

WARNING: This might have side-effects in places where the empty string
is relevant.

But now it is possible to compute the tables and centralizers are
no longer bigger than the whole group.

gap> CharTable("WeylD", 3);
rec( name := "W(D3)", order := 24, centralizers := [ 24, 8, 4, 4, 3
 ], orders := [ 1, 2, 2, 4, 3 ], powermap :=
[ , [ 1, 1, 1, 2, 5 ], [ 1, 2, 3, 4, 1 ] ], irreducibles :=
[ [ 3, -1, -1, 1, 0 ], [ 1, 1, -1, -1, 1 ], [ 3, -1, 1, -1, 0 ],
  [ 2, 2, 0, 0, -1 ], [ 1, 1, 1, 1, 1 ] ], classparam :=
[ [ 1, [ [ 1, 1, 1 ], [  ] ] ], [ 1, [ [ 1 ], [ 1, 1 ] ] ],
...

Goetz Pfeiffer.

PS: a detailed description of the implementation of the character
tables of Weyl groups and related groups will soon be available via
anonymous ftp from 'samson.math.rwth-aachen.de'.