> < ^ Date: Mon, 25 Jul 1994 08:41:00 WST
> < ^ From: Dmitrii Pasechnik <d.pasechnik@twi.tudelft.nl >
> ^ Subject: Re: Read() (Rather Subgroup(...

Dear Forum,

Let g:=Group(....). Is there any natural way to avoid calling a procedure
checking whether h:=Subgroup(g,[...]) is indeed a subgroup in the
moment of creating h?

As we were told, this checking might be rather expensive if the
generators of h does not form a subset of g.generators.

Suppose one knows that the generators of h are words in g.generators.
Then a strange way to create h fast is to add these words into
Can it be avoided?

For instance, if g is a matrix group, there are no efficient ways to
check that h<=g, so in fact I several times ran into this problem,
when I created a subgroup of a matrix group, and
gave up without understanding what went wrong.


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