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Re: Problem with matching.

• To: mathgroup at smc.vnet.net
• Subject: [mg53930] Re: [mg53907] Problem with matching.
• From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
• Date: Fri, 4 Feb 2005 04:11:45 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

>-----Original Message-----
>From: Josef Karthauser [mailto:joe at tao.org.uk] 
To: mathgroup at smc.vnet.net
>Sent: Thursday, February 03, 2005 12:11 AM
>To: mathgroup at smc.vnet.net
>Subject: [mg53930] [mg53907] Problem with matching.
>
>Can someone tell me why this doesn't match?
>
>F[{x, 2, c}]F[{x, 1, f}] /. F[{___, a_, ___}]F[{___, a_, ___}] :> yes
>
>I'm expecting 'yes' to be returned if any of the list 
>arguments to F[] contain the same value.  It doesn't match 
>however; what am I doing wrong?
>
>Thanks,
>Joe
>--
>Josef Karthauser (joe at tao.org.uk)	       http://www.josef-k.net/
>FreeBSD (cvs meister, admin and hacker)     http://www.uk.FreeBSD.org/
>Physics Particle Theory (student)   http://www.pact.cpes.sussex.ac.uk/
>================ An eclectic mix of fact and theory. =================
>
>
>

In[2]:= F[{x,2,c}]F[{x,1,f}] /.
	HoldPattern[F[{___,a_,___}]F[{___,a_,___}]] :> yes

Out[2]= yes


The first argument of Rule or RuleDelayed is evaluated before
application of the rule. HoldPattern prevents this.


Such your pattern first became 

In[3]:= F[{___, a_, ___}]F[{___, a_, ___}]

Out[3]= F[{___, a_, ___}]^2

which then of course didn't match.


--
Hartmut Wolf