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Replacement rules in NonCommutative Algebra Package

  • To: mathgroup at
  • Subject: [mg13748] Replacement rules in NonCommutative Algebra Package
  • From: Nam-Anh Nguyen <anh at>
  • Date: Wed, 19 Aug 1998 01:38:35 -0400
  • Sender: owner-wri-mathgroup at

Hi experts,

I've been using NonCommutative Algebra package for alsmost one year and
well aware of the fact that the Mathematica replacement operator /. ->
does not work appropriately within this package. Instead I must use the
Substitute command of this NCAlgebra package.

However I've impression that this command does not allow one to work
with replacement rules that contain conditions

For instance, after loading the package I enter

and the result is

which is correct




    Substitute[x**a**b,a**b->c/;CommutativeQ[a]] gives

which is not correct. (It should give the original expression, i.e.
x**a**b, as the condition  fails)

Is that a bug??
Any suggetion??

Thank you for your help


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