Re: Infinity vs DirectedInfinity[1]

*To*: mathgroup at smc.vnet.net*Subject*: [mg70543] Re: [mg70489] Infinity vs DirectedInfinity[1]*From*: "Chris Chiasson" <chris at chiasson.name>*Date*: Thu, 19 Oct 2006 03:22:06 -0400 (EDT)*References*: <200610180816.EAA07979@smc.vnet.net> <45362BB8.9080006@wolfram.com>

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 wolfram.com> 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 > -- http://chris.chiasson.name/

**References**:**Infinity vs DirectedInfinity[1]***From:*"Chris Chiasson" <chris@chiasson.name>