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Re: Defining a flat, orderless, one-identical function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28096] Re: [mg28046] Defining a flat, orderless, one-identical function?
  • From: Ralph Benzinger <mma-l at endlos.net>
  • Date: Fri, 30 Mar 2001 04:12:52 -0500 (EST)
  • References: <200103290824.DAA03033@smc.vnet.net> <B6E8D3A8.BC10%andrzej@platon.c.u-tokyo.ac.jp>
  • Sender: owner-wri-mathgroup at wolfram.com

On March 29, you wrote:
> This is a rather complex issue tha thas been already discussed in some
> detail a number of times so you shoudl search the archives to understand
> more.

Thanks for pointing this out; I admit I did a shoddy job in
searching the archives.  I've now found a series of article from
January 2000 that pretty much settle the issue once and for all. 
There also was an inquiry from 1995 and an interesting solution
from Wolfram's support staff that suggested removing the Flat
attribute and adding definitions that would unfold nested function
calls manually.

> Here is just one solution to your problem, the main idea of which, if
> I remeber correctly, was once suggested by Carl Woll: [...]
>
> In[2]:=
>    (x_max/;Length[Unevaluated[x]]==1):=Hold[x][[1,1]]

Great! This ingenious rule works like a charm.  It's quite a hack,
though, isn't it? ;-)

Ralph

-- 
Ralph Benzinger          "This is my theory, it is mine, I own it,
Cornell Univeristy        and what it is, too." -- Ann Elk (Mrs.)


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