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Re: Re: More /.{I->-1} craziness

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  • Subject: [mg106094] Re: [mg106035] Re: More /.{I->-1} craziness
  • From: Murray Eisenberg <murray at>
  • Date: Fri, 1 Jan 2010 05:35:38 -0500 (EST)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <hhf5s3$h4o$> <>
  • Reply-to: murray at

"What you see is not what is acted upon".  That's a wonderful synopsis 
of the situation!  (Except that perhaps I would insert the word 
"necessarily" before "what".)

I haven't searched the docs, but something like that needs to be stated, 
explained, and exemplified some place, or places, in the Documentation 
Center that is easily found.

Now that the printed "The Mathematica Book" is gone and replaced by a 
non-linear web of documentation, finding where to expose such a 
principle is unclear.

Alexander Elkins wrote:
> ... what you see is not what is acted upon, for example:
> In[2]:= FullForm[{1/-2,I,-I,1+I,1-I,1/-2+I/-3}]
> Out[2]//FullForm=
> List[Rational[-1,2],Complex[0,1],Complex[0,-1],Complex[1,1],Complex[1,-1],Co
> mplex[Rational[-1,2],Rational[-1,3]]]
> In other words -I is seen as Complex[0,-1] not -Complex[0,1], Complex[0,1]
> does not match anything, so no replacement is performed leaving the input
> unchanged. 

Murray Eisenberg                     murray at
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

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