On Sun, 07 Dec 2008 16:24:58 -0800, George Sakkis wrote: > On Dec 7, 6:37 pm, Steven D'Aprano <[EMAIL PROTECTED] > cybersource.com.au> wrote: ... >> Given: >> >> x = log(-5) # a NaN >> y = log(-2) # the same NaN >> x == y # Some people want this to be true for NaNs. >> >> Then: >> >> # Compare x and y directly. >> log(-5) == log(-2) >> # If x == y then exp(x) == exp(y) for all x, y. exp(log(-5)) == >> exp(log(-2)) >> -5 == -2 >> >> and now the entire foundations of mathematics collapses into a steaming >> pile of rubble. > > And why doesn't this happen with the current behavior if x = y = log > (-5) ? According to the same proof, -5 != -5.
You're right, I was a little sloppy in my "proof". There are additional subtleties going on. -- Steven -- http://mail.python.org/mailman/listinfo/python-list