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Re: replacement x->y except in Exp[x]

• To: mathgroup at smc.vnet.net
• Subject: [mg110900] Re: replacement x->y except in Exp[x]
• From: Andrzej Kozlowski <akozlowski at gmail.com>
• Date: Sat, 10 Jul 2010 06:33:07 -0400 (EDT)

Actually I is a Symbol, before evaluation:

In[90]:= Head[Unevaluated[I]]

Out[90]= Symbol

but it is no loner one after evaluation:

In[91]:= Head[I]

Out[91]= Complex

Andrzej Kozlowski


On 10 Jul 2010, at 17:01, Murray Eisenberg wrote:

> I is not a "symbol"!
> 
> Head[I]
> Complex
> 
> 3+I /. I-> -I
> 3 + I
> 
> Head[2]
> Integer
> 
> (2/3) /. 2->5
> 2/3
> 
> Please stop beating the dead horse.
> 
> 
> On 7/8/2010 8:34 PM, AES wrote:
> 
>> ...Is it ever a good idea to use ReplaceAll to do word-processing-type
>> "global find and replace" changes like this?
>> 
>> Lengthy threads on this NG have pointed out the havoc that this can
>> wreak if the symbol I is among those replaced, particularly if one
>> attempts to do I ->  -I.
>> 
>> Or is I the _only_ symbol in the entire Mathematica vocabulary that
>> encounters this difficulty?
>> 
>> (I really would like to know the answer to this question, even if this
>> is entirely out of curiosity, not any real need.  I've asked it
>> previously, and never gotten an answer.)
> 
> 
> -- 
> Murray Eisenberg                     murray at math.umass.edu
> Mathematics & Statistics Dept.
> Lederle Graduate Research Tower      phone 413 549-1020 (H)
> University of Massachusetts                413 545-2859 (W)
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>