[isabelle-dev] lex_prod changes

Lawrence Paulson lp15 at cam.ac.uk
Thu Aug 20 22:42:58 CEST 2020

As somebody who’s wasted a week trying to do this, I can’t say that I like it myself.


> On 20 Aug 2020, at 21:27, Bertram Felgenhauer <bertram.felgenhauer at googlemail.com> wrote:
> Hi,
> I've gotten some emails from Jenkins lately and finally taken a moment
> to investigate.
> Apparently, R1 <*lex*> R2 was changed to artificially impose
> irreflexivity on R1 (checking  a ~= a'  in addition to  a R1 a').
> What are the benefits of doing this? There is a (heavy, to me)
> downside: It destroys the property that the lexicographic product is
> transitive if both input relations are. More fundamentally, while in
> the previous formulation, the lexicographic product was a meaningful
> and useful operation for quasi-orders, now that use case is closed
> off.
> Was this change discussed in advance? I may have missed it... in any
> case I strongly dislike it.
> Cheers,
> Bertram
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