Regexes, Canonical Equivalence and Backtracking of Input

Philippe Verdy verdy_p at
Tue May 19 07:58:33 CDT 2015

2015-05-19 2:44 GMT+02:00 Richard Wordingham <
richard.wordingham at>:

> > Good books on the subjext are now becoming difficutlt to find (or
> > they are more expensive now), and too difficult to use on the web
> > (for such very technical topics, it really helps to have a printed
> > copy, that you an annotate, explore, or have beside you instead of on
> > a screen (and printing ebooks is not an option if they are
> > voluminous). May be you have other books to recommend.
> Google Books, in English, gives access to a very helpful chapter on
> regular languages in trace monoids in 'the Book of Traces'.

It's interesting to see that books on this topic were published mostly
after 1994. As I terminated my training cursus at this period, the subject
was largely not covered before; now that I live in a small city where
there's no good scientific library finding just some books in English on
such topics is extremely rare (the only books I see are those published in
French in the "for Dummies" series and I find them completely
ininteresting. As a consequence I buy much less scientific books now.

However Wikipedia is not a convenient place for extensive (but progressive)
coverage of a topic (the one page limit has a consequence: it's difficult
to learn from these articles, and you can read them only if you already
know most of its covered topics or you don't need to navigate randomly over
many pages through random links). Wikiepdia remains useful only if you can
isolate your search to a few smaller subtopics. Wikibooks and Wikisource
would be more useful for such extensive studies, but their contents is very
small (and for legal resons, Wikisource cannot contain many scientific
books about theories that were written after WW2 : unfortunately this
covers almost all researches being performed on comuting theories that
exploded only after th 1960's, and in many areas the researches were also
protected by extensive patents in addition to copyrights; so the
interesting books are published in English, extremely rarely translated,
have a limited distribution, they are also expensive and not found except
in very few libraries and only in some cities that have a scientific
university ; public libraries also don't have these books, which are too

Now there's the net, but even Google books only exposes just some pages
(for the rest, Google books propose books that are even more expensive than
on normal libraries, and from random sellers that are frequently not
trustable : e.g. I will never buy anything from Amazon if Amazon is not the
seller, or from other similar large platform on which you don't know who is
the seller, or because the seller also wants us to pay absive
delivery/shipping costs without even giving any warranty on the product and
without even allowing us to trace the command; there are too many abusers,
or that sell products with severe defects; I prefer using French online
selling platforms; in addition this saves money on taxes if the seller is
in the EU, otherwise we experiment long delivery delays in tex customs, and
we also need to pay the tax on delivery, in addition to the initial cost,
plus the currency change fees by the bank; all these can easily double the
total cost, but at end there's also a big deception on the product and it's
impossible to return it and get a refund)

In summary, it is really bad that libraries are disappearing in many
places, or are reducd to sell only a limited catalog "for the dummies" or
popular books advertized in the medias. The variety of available books for
sale is dramatically decreasing now.

The net cannot replace these books that you want to read slowly and keep as
reference for later reuse... except if the e-books you can buy online offer
an option to get a "print on demand" with a good quality with reasonable
costs and delays for the delivery (some French editors are proposing this
"on demand printing" service, even for books from some other foreign
editors). Note that is is not limtied to just scientific books, the system
could be used for delivering all kinds of books (including litterature,
photography, magazines, newspapers, or rare research papers available only
in one public university library that could get some fees helping them to
renew their own purchases...)
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