See also https://github.com/sympy/sympy/issues/17224
On Sun, 4 Aug 2019 at 13:32, Chris Smith <smi...@gmail.com> wrote: > > Symbols default to commutative=True but I wonder if we should also default to > `finite=True` since that is consistent with the behavior of `x - x` being 0. > (If x is infinite then `x - x` is nan.) In this discussion here I point out > how `x-x->0` without the correct assumption (that x is finite) is > inconsistent with unevaluation of `x**2 < 0`. The inequality remains > unevaluated because it would be an invalid comparison if `x` had real and > imaginary components and produced a comparison like `2*I < 0` when `x = 1 + > I`. > > I suspect that this might have minimal impact on the current behavior; I > suspect that making `real=True` a default assumption, too, would have a > greater impact. Without making the latter, all inequalities would continue to > be unevaluated for plain/vanilla symbols because they would have to entertain > the possibility of an invalid result. e.g. `Eq(1/x, 0)` for finite `x` would > not evaluate to True (even though `x` might be finite) when x is not known to > be real or imaginary. > > /c > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sympy+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/12753973-4620-4b2e-8046-8147b4ec2372%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAHVvXxTfRYeT8PGvFYBFQTVD%2B8ZX5LGhGnUsVSyYauFJujBx%3Dg%40mail.gmail.com.
