In Maple 'is' is part of the assume mechanism http://www.maplesoft.com/support/help/maple/view.aspx?path=assume
and returns True, False or FAIL (if it cannot determine whether the property is always satisfied). Maple also has 'evalb' and 'testeq' with somewhat different semantics. Are you proposing a similar "tristate" logic in Sage? Is there somewhere that I can find "Truth(tm)"? On 25 September 2015 at 02:09, Ralf Stephan <gtrw...@gmail.com> wrote: > On Thursday, September 24, 2015 at 8:22:53 PM UTC+2, Bill Page wrote: >> >> What answer should be expected when it is not possible to show that an >> expression is zero? Would you expect that >> >> ex.is_zero() = not(ex.is_nonzero()) ? > > > Yes, for constant expressions (i.e. not containing symbols) at the moment. > With new code, yes for all expressions. > >> >> I suppose that I should expect True or False from >> >> bool(ex=0) >> >> and False in the case that it cannot be shown to be true. > > (assuming you meant bool(ex==0)) > If you expect that then don't be surprised when innocent code > behaves wrongly and uses unnecessary time, because the > function that gets called will also get called with e.g. if (ex):... > > Having an explicit function for showing Truth(tm) will prevent > this. > >> >> But I am not >> so sure about is_... Do you expect only two possible outcomes and an >> runtime error in the case of a failure to decide one or the other? > > > Having an explicit function for showing Truth(tm) will allow it > to have three results: Yes/No/NotImplemented > (Exceptions for things like complex x > 0). > > Ticket #17700 proposes tristate logic, SymPy has it too. > > The question is if we should call it is(). > I just found that Maple too uses that name, so please voice any > final objections. > > -- > 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 http://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 http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
