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Re: Pattern matches only when named

• To: mathgroup at smc.vnet.net
• Subject: [mg43908] Re: Pattern matches only when named
• From: Oliver Friedrich <oliver.friedrich at tzm.de>
• Date: Sat, 11 Oct 2003 01:33:28 -0400 (EDT)
• Organization: TZ Mikroelektronik
• References: <bm2ugv$6so$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Ken Morgan <kemorgan at vt.edu> wrote in news:bm2ugv$6so$1 at smc.vnet.net:

> Just a curiosity:
> 
> In[1]:=   f + g /. u_ + _ -> h
> Out[1]:=  h
> 
> but
> 
> In[2]:=   f + g /. _ + _ -> h
> Out[2]:=  f + g
> 
> Why does the pattern match only when one of the Blanks has a name?
> 
> 
> Thanks,
> Ken
> 
> 

Hi Ken,

In your second example the blank stands for an idendical expression. So 
this pattern matches only when both expressions left and right from the 
plus are the same. Try f+f/._+_->h and look what happens.

You're welcome ;-)

Regards

Oliver Friedrich