Classification of group extensions For hours I have been looking for Claude Archer, Classification of group extensions, PhD thesis, Université Libre de Bruxelles, 2002, but I found nothing.
Is there any replacement for this thesis, I mean another article or maybe a book about this topic ?
 A: A friend of mine sent me your post about my Phd thesis.
Indeed i partially implemented in GAP at that time (12 years ago) to produce the results table in my Phd.
Provide me an email adresse and i will send you a copy.
Also Derek Holt, Warwick University UK, where i did my postdoc, had an electronic copy.
best regards 
claude
A: No, not really. Well, of course there are many books and articles on the topic of groups extensions. But Claude Archer's thesis contains some unique material that is not covered by anything else, to the best of my knowledge.
This thesis was never published, and is indeed very hard to find. I wanted to get hold of an electronic copy, but I was neither able to reach Claude Archer (he left university around 2003 and has been out of touch since then), nor did his advisor have an electronic (though apparently the library of the ULB will eventually scan it -- but this could still be a couple years out...). I know of one paper copy outside of the library of the ULB (in the possession of  Bettina Eick, who was on Claude Archer's defense committee), which one of these days I hope to be able to replicate using a photo copier... or perhaps instead of that I could scan it. But before I can attempt either, I will have to travel to the place with the paper copy is right now, not sure when it will get to that... ;-).
The reason why I am interested in it: Some time ago, Bettina and me started work on a project for constructing various kinds of group extensions with computer help in a more effective way than done by current algorithms. We did quite some work on solvable groups. But for the cases of non-solvable groups, it seems that Claude Archer's work is better than what is currently being implemented in systems like Magma or GAP, and what is described elsewhere, and possibly better than what we had cooked up ourselves until then (or perhaps not better, but equivalent, I am not quite sure). Anyway: Besides other things, he apparently constructed all non-solvable groups of order up to 23,000 from the existing tables of perfect groups. Nice.
That nobody is implementing his work, or (to my knowledge) is building upon it, is likely due to the facts that (a) the thesis is very hard to come by (luckily, Bettina has a copy) (b) has not even been partially published in the form of articles and (c) it is not exactly the best write-up of a mathematical idea I have seen (to put it carefully...). In particular, I am not 100% sure how much better than existing ideas his work really is... Still, as far as I know, there is no replacement for his work anywhere. There really are some things in there which I have not seen anywhere else...
It would be awesome if (a) somebody could make an electronic copy of it available (I don't look forward to scanning / copying hundreds of pages myself ;-), and/or (b) make a fresh, concise write up of the ideas in it (I don't hold my hopes up on that; I guess it would have to be part of a text book or a survey article, but it might be to specialized to be suitable for that).
Ah well. Sorry for not really being more helpful, but I hope I made it clear why the situation is somewhat complicated.
