I am reading this differently, but that may be my lack of knowledge of English.
I thought "Return True, unless provably zero" would give true, if something cannot be shown to be zero. Martin On Tuesday, 27 September 2022 at 12:21:12 UTC+2 vdelecroix wrote: > On Tue, 27 Sept 2022 at 11:58, 'Martin R' via sage-devel > <sage-...@googlegroups.com> wrote: > > > > > > > > On Friday, 23 September 2022 at 20:09:55 UTC+2 Nils Bruin wrote: > >> > >> On Friday, 23 September 2022 at 10:37:01 UTC-7 axio...@yahoo.de wrote: > >>> > >>> OK, this is off topic, but: shouldn't it be this convention? At least: > shouldn't there be some convention? Maybe it would be good to discuss this > in a separate thread. Thus, I repeat the question: > >>> > >>> Is there, or should there be a convention about x._bool_ returning > False only when x is provably False? > >>> > >> No, quite the opposite. Certainly in SR, equalities that can't be > proven correct (for "proof" used in the loose sense of what the various > symbolic engines are willing to confirm), will return "False" when > converted to "bool" value. The key is: _bool_ cannot really error out (that > would break too much in python) and does not allow for "unknown" outcomes, > so some choice must be made. > > > > > > The doc of Expression.__bool__ says: > > > > Return True unless this symbolic expression can be shown by Sage > > to be zero. Note that deciding if an expression is zero is > > undecidable in general. > > > > which seems to be in agreement with what I thought. Or am I missing > something? > > > > It seems really strange to me that "not O(x^7)" should be True. > > According to this symbolic specification,O(x^7) is not provably an > exact zero so it is reasonable to evaluate it to False. Which means > that "not O(x^7)" ought to be True. > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/a4a00641-0b8d-4fd4-8690-7e75bb860c74n%40googlegroups.com.
