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Re: ReplaceAll question

  • To: mathgroup at
  • Subject: [mg82562] Re: ReplaceAll question
  • From: Albert <awnl at>
  • Date: Wed, 24 Oct 2007 04:37:02 -0400 (EDT)
  • References: <ffkf46$sh6$>

Yaroslav Bulatov wrote:
> b = 3;
> Hold[a[[b]]] /. {b -> c}
> ReplaceAll has no effect, why? 

Because the rule b -> c is evaluated to 3 -> c
before it is applied, and the latter doesn't
match anything, which at least is better than
to match something that shouldn't...

> What is the recommended way of carrying
> out the replacement above?

Hold[a[[b]]] /. {HoldPattern[b] -> c}



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