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MathGroup Archive 2004

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Re: Question on pattern matching

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47807] Re: Question on pattern matching
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Tue, 27 Apr 2004 04:47:47 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 4/26/04 at 2:40 AM, rgreen at mail.ru (Roman Green) wrote:


>In the following Mathematica's output In[1]:= SetAttributes[k,
>Orderless] 

>In[2]:= k[a, b, b] /. k[x_, x_, y_] -> 0 
>Out[2]= 0
>In[3]:= k[a, b, b] /. k_[x_, x_, y_] -> 0 
>Out[3]= k[a, b, b]

>I can't understand why Mathematica can find match when applying
>pattern k[x_, x_, y_], but is unable with more general pattern
>k_[x_, x_, y_].

The pattern k_ matches an expression named k with any head

k[a, b, b] is an expression with head k and no name. The two things don't match which is why you get the output you got.

The pattern _k is any expression with head k. So,

k[a,b,b]/._k->0

will result in what you were expecting
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