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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Wed, 17 Sep 2014 09:34:14 -0600
Subject: Re: Why `divmod(float('inf'), 1) == (float('nan'), float('nan'))`
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On Wed, Sep 17, 2014 at 9:29 AM, Chris Angelico <rosuav@gmail.com> wrote:
> On Thu, Sep 18, 2014 at 1:16 AM, cool-RR <ram.rachum@gmail.com> wrote:
>> I didn't ask for the modulo, I agree it should remain NaN. I'm talking about the floor division.
>>
>
> Invariant: div*y + mod == x.
>
> If mod is NaN, there is no possible value for div that will make the
> invariant true, ergo it too has to be NaN.

That still doesn't make the invariant true. By this argument div could
be 42, and the invariant would hold equally well (i.e. not at all).