I think that x.__bool__ should return True only if x is *known* to be zero.
I have three docstrings that support this view: rings/real_mpfi.pyx\03905: def __bool__(self): rings/real_mpfi.pyx\03906- """ rings/real_mpfi.pyx\03907- Return ``True`` if ``self`` is not known to be exactly zero. rings/real_mpfi.pyx\03908- -- rings/complex_interval.pyx\01495: def __bool__(self): rings/complex_interval.pyx\01496- """ rings/complex_interval.pyx\01497- Return ``True`` if ``self`` is not known to be exactly zero. rings/complex_interval.pyx\01498- -- symbolic/expression.pyx\03310: def __bool__(self): symbolic/expression.pyx\03311- """ symbolic/expression.pyx\03312- Return True unless this symbolic expression can be shown by Sage symbolic/expression.pyx\03313- to be zero. Note that deciding if an expression is zero is and I have not found a docstring contradicting this point of view. However, the behaviour of (fixed precision) power series is different: sage: R.<t> = QQ[[]] sage: f = t.add_bigoh(5) - t sage: f O(t^5) sage: not f True I think that this is a bug. One implication is, as noticed by Chris Wuthrich, that the product "x * y" is not necessarily zero, even if "not x" gives True. Before trying to create a branch, I'd like to hear other opinions. Martin -- 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/5ad675ea-1cf1-4ea5-a39d-40eb567ff2e9n%40googlegroups.com.
