On Tue, Nov 15, 2016 at 08:53:43AM +0100, Vincent Delecroix wrote: > Not currently (though we have "Unknown"). The main problem is the > interaction with Python booleans and the operators "or", "and", "not" > (which are *not* logical operators). The Sage "Unknown" is badly > broken for these reasons > > sage: not Unknown # waiting for Unknown > True > sage: Unknown or False # waiting for Unknown > False > > So be careful if you start using it! > > If we would use the correct logical operators ~ (for negation), ^ (for > xor) and & (for and) then we might be able to come up with something. > But Sage sort of ignore them. > > This problem has been discussed a lot on this mailing list and there > even exists a (refused) PEP request in this direction.
For reference, it is https://www.python.org/dev/peps/pep-0335/ (the main reason for rejecting the proposal was "too much discussions"...). Perhaps was the proposal too greedy, so i wonder whether there would be a possibility to have a trool adding an Unknown to bool that does not perturb the speed when only True and False are used, and so that the "short-circuiting semantics" remains preserved. This could indeed be useful in testing equality of overlaping real-intervals, undecidable problems in groups, equality of symbolic expressions, ... Ciao, Thierry > Best, > Vincent > > > > On 15 November 2016 at 08:22, Thierry Dumont <tdum...@math.univ-lyon1.fr> > wrote: > > When developing a software which aims to prove something, it seems > > necessary to be able to return something in > > {True, False, Indeterminate}. > > > > Of course, there are many possibilities to do this, but is there a > > "canonical" one in Sage ? > > > > In C++, for example, there exists the Boost Tribool library > > (http://www.boost.org/doc/libs/1_62_0/doc/html/tribool.html#tribool.introduction) > > . > > > > t.d. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "sage-devel" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to sage-devel+unsubscr...@googlegroups.com. > > To post to this group, send email to sage-devel@googlegroups.com. > > Visit this group at https://groups.google.com/group/sage-devel. > > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To post to this group, send email to sage-devel@googlegroups.com. > Visit this group at https://groups.google.com/group/sage-devel. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
