[isabelle-dev] Proper sign of gcd / lcm on type int

Pierpaolo Bernardi olopierpa at gmail.com
Fri Jun 3 22:17:22 CEST 2016

About signs in divisions etc. I found the following paper very useful:


Maybe someone else will find it useful too.


On Fri, Jun 3, 2016 at 9:29 PM, Makarius <makarius at sketis.net> wrote:
> On 03/06/16 18:49, David Matthews wrote:
>> The Poly/ML implementation was based on the idea that something called a
>> "multiple" ought to follow the usual rules of multiplication; nothing
>> stronger than that.  I don't think I found anything that indicated what
>> the sign should be.  The GCD code uses GMP's GCD if possible; the LCM
>> code is just derived from that.
>> I have no strong opinions on this and I'm happy to change it.  There's
>> also the question of whether to add it to the IntInf structure and
>> signature despite the incompatibility with the "official" library
>> definition.
> How is the situation wrt. planned updates of the SML Basic Library
> specification?
> Maybe this is a chance to add IntInf.gcd and IntInf.lcm officially,
> which a clear specification about the sign, whatever that might be.
>         Makarius
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