> < ^ Date: Wed, 23 Jun 1999 15:12:56 +0200 (CEST)
> < ^ From: Thomas Breuer <Thomas.Breuer@Math.RWTH-Aachen.DE >
< ^ Subject: Re: Second maximal of Co1, About Semidirect products

Dear Gap Forum,

Stefan Kohl wrote

In this example, the character table can be fetched from the
library via

gap> tbl:= CharTable( "3.Suz.2" );
CharTable( "3.Suz.2" )

I just want to make a small, rather technical remark here :
The function `CharTable' is only defined in GAP 3,
in GAP 4 it is called `CharacterTable' (and is, by the
way, not yet documented in GAP 4 beta 5).

Changes of variable names such as this one are listed in Section
``Changed Variable Names'' of Chapter ``Migrating to GAP 4'' in
the GAP 4 Tutorial.

Concerning the examples for semidirect product
constructions also given by Thomas Breuer :
There is no function `PermGroup' to convert
a given group to a permutation group in GAP 4,
this also works only in GAP 3 up to now.

Section ``Isomorphisms vs. Isomorphic Structures'' of the same
chapter in the GAP 4 Tutorial describes how to get different
representations of groups.
For example `IsomorphismPermGroup' can be used to construct an
isomorphism to a permutation group, and this permutation group
can then be accessed with `Image'.

In GAP 4, there is also no method for
`ExtraspecialGroup(IsPermGroup, ...)',
as far as I have seen, this works only for the
default category `IsPcGroup'.

Also GAP 3 did not provide the possibility to get a permutation
group as result of a call to `ExtraspecialGroup'.
As in the situation above, one can use `PermGroup' (in GAP 3)
or `IsomorphismPermGroup' and `Image' (in GAP 4)
--although it is probably not a good idea to use a permutation
representation when dealing with an extraspecial group.

Kind regards,
Thomas Breuer

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