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Re: Infinity vs DirectedInfinity[1]

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  • Subject: [mg70543] Re: [mg70489] Infinity vs DirectedInfinity[1]
  • From: "Chris Chiasson" <chris at>
  • Date: Thu, 19 Oct 2006 03:22:06 -0400 (EDT)
  • References: <> <>

Carl Woll

This is the conclusion I came to after talking with Andrzej Kozlowski
(I also posted about it -- though it won't go out until tomorrow
because I sent it maybe an hour ago)

What I find interesting is that Andrzej said you would probably reply
and that I would then have a definitive answer.

Thank you.

P.S. One interesting question that came up when we were emailing
off-list was: "How was formatting done before the box formatting
system was introduced?"

On 10/18/06, Carl Woll <carlw at> wrote:
> Chris Chiasson wrote:
> >Infinity is a symbol, as far as I know. However, in FullForm it is
> >shown as the equivalent DirectedInfinity[1].
> >
> >Is there some kind of MakeBoxes rule for FullForm that makes Infinity
> >show up that way?
> >
> >
> >
> Actually, when evaluated, Infinity is converted to DirectedInfinity[1].
> This is like when I is converted to Complex[0,1]. Compare:
> FullForm[Hold[Infinity]]
> Hold[Infinity]
> and
> FullForm[Infinity]
> DirectedInfinity[1]
> On the other hand, DirectedInfinity[d] has formatting rules for
> InputForm, StandardForm and TraditionalForm that cause it to be
> displayed as Sign[d] Infinity when d is +/-1 or +/-I.
> Carl Woll
> Wolfram Research


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