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Dear Gap-forum,

In a letter to the Forum on 22 April 1996, Volkmar Felsch wrote:

As described in the manual section 'Tietze Transformations', each

presentation record, 'P' say, carries with it certain parameters,

the so-called 'Tietze options'. One of these is the parameter

'P.generatorsLimit' which by default is initialized to be zero.

Its purpose is to prevent the Tietze transformations functions

from eliminating too many generators.More precisely: The functions 'SimplifyPresentation', 'TzGo', and

'TzGoGo' are not allowed to eliminate a generator if the resulting

number of generators would be smaller than this bound.

However, it does appear that SimplifyPresentation(P) will eliminate a

generator found to be trivial, even if P.generatorsLimit has first

been set to Length(P.generators). This certainly can cause me

problems when I need there to be a bijection between two sets of

generators, even if one of the generators turns out to be trivial. Is

there any way to prevent SimplifyPresentation from removing trivial

generators? Am I right in assuming that the function TzSearch would

not do this?

Thanks for your help.

Regards, Leonard.

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