On Tue, 27 Sept 2022 at 11:58, 'Martin R' via sage-devel <sage-devel@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/CAGEwAAk_-fXfQpvj4YUnemJu3T3%3DJ%2BGJUuVrKa6whBHfqZAQOw%40mail.gmail.com.
