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Re: Pattern matches only when named

• To: mathgroup at smc.vnet.net
• Subject: [mg43900] Re: Pattern matches only when named
• From: "wouter meeussen" <wouter.meeussen at pandora.be>
• Date: Fri, 10 Oct 2003 03:06:21 -0400 (EDT)
• References: <bm2ugv$6so$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

FullForm[  _ + _ -> h]

Rule[Times[2, Blank[]], h] (* both blanks need be equal *)



FullForm[  u_ + _ -> h]

Rule[Plus[Blank[], Pattern[u, Blank[]]], h] (* both can be different, or not
*)



Wouter.





"Ken Morgan" <kemorgan at vt.edu> wrote in message
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
>