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how implement a rule

  • To: mathgroup at
  • Subject: [mg112568] how implement a rule
  • From: Murray Eisenberg <murray at>
  • Date: Mon, 20 Sep 2010 05:43:34 -0400 (EDT)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • Reply-to: murray at

I want to define a function abs (mimicking Abs) with various properties. 
One part of the definition is:

   abs[c_ z_ /; c \[Element] Reals] = Abs[c] abs[z]

Given that, how might I express that abs[z] is always real in such a way 
that the result of


will be 1/abs[z]^2 -- WITHOUT explicitly introducing, say:

   abs/: abs[1/abs[z_]^2] =  1/abs[z]^2


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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