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Dima Pasechnik writes in his e-mail message of 1993/11/15

To the best of my knowledge, the following by-product of the use of ^C

while computing strong generators for a permutation group should not

occur.Let G be a permutation group defined by a list of generators, and let the

first function called after the definition of G be Size(G). I press ^C^D

before it finishes, then call Size(G) again. It returns an answer

instantly, since G.size is already defined. Moreover, sometimes G.size is

wrong in this case. I beleive that G.size should actually be undefined.

At least I don't know of any place in the GAP manual mentioning such

effects.

This is a know bug (calling is an unwanted by-product is very nice ;-).

The problem is that as soon as GAP starts to compute a stabilizer chain

it enters this in the group record. When the computation of the

stabilizer chain is interrupted the group record thus contains an

unfinished and sometimes incomplete stabilizer chain. This is a bug.

The stabilizer chain should not be entered in the group record until it

is complete.

'Size' only sees that the group records has a stabilizer chain and

returns the product of the indices. This is correct but only under the

assumption that the stabilizer chain is complete. Other functions for

permutation groups will also fail with such an incomplete stabilizer

chain (and their failure may be more difficult to detect).

Fixing this problem is planned for the next release of GAP. I am sorry

but I cannot offer an immediate solution or workaround. Just be careful

and keep a healthy distrust for results computed by GAP.

Martin.

-- .- .-. - .. -. .-.. --- ...- . ... .- -. -. .. -.- .- Martin Sch"onert, Martin.Schoenert@Math.RWTH-Aachen.DE, +49 241 804551 Lehrstuhl D f"ur Mathematik, Templergraben 64, RWTH, 52056 Aachen, Germany

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