The GAP package ITC Version 1.0
It is a pleasure to announce the acceptance of the ITC share
package by Volkmar Felsch, Ludger Hippe, and Joachim Neubuser.
The package is an interactive Todd-Coxeter program which allows the
user to execute interactively single steps in an enumeration of the cosets
of a subgroup of a finitely presented group. The package uses the XGAP
graphics surface to display the coset table, relation tables, subgroups
tables etc. in separate windows and so allows the user to see the progress
of the enumeration step by step as it progresses.
ITC allows the user to display the coset table, subgroup and relation
tables and to make definitions of coset numbers by clicking in these.
It also can display auxiliary tables such as the list of definitions
made, the list of "gaps of length 1" or the list of pending coincidences.
Some of the main strategies of coset enumerations such as HLT,
Felsch and minimal gap strategies are available in the ITC and can either
be used to try to close the tables or to make a prescribed number of
definitions using these strategies. The package also contains two
operations for a posteriori "pruning" a definition sequence if
coincidences have occurred. Scrolling of the tables allows the user
to handle tables much bigger than would fit on the screen.
The package also contains a number of examples which can be input
directly and the manual gives excellent information on experimenting
This is a first version of ITC. Later versions will have the coset table in a
separate window from the control window which will display the control
buttons and message line. The authors also intend to add further
functionality to later versions.
Note: ITC V1.0 requires GAP 4.2 and XGAP V4r11
The package will be available via the GAP 4 share packages web page:
and in the GAP 4 share packages ftp directory:
as well as from the respective mirrors.
Edmund F Robertson
The GAP Council
2 March 2000