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Re: Why does MemberQ[{0,1,2}, expr_] evaluate to True?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125913] Re: Why does MemberQ[{0,1,2}, expr_] evaluate to True?
  • From: Christoph Lhotka <christoph.lhotka at fundp.ac.be>
  • Date: Fri, 6 Apr 2012 06:01:55 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <4F7D8716.4010202@fundp.ac.be>

I am really sorry for reposting it but of course the subject of 
discussion should be:

MemberQ[{0, 1, 2}, expr_]

Please replace below and in message ModuleQ by MemberQ.

best,

christoph



On 04/05/2012 01:50 PM, Christoph Lhotka wrote:
> Hello,
>
> I found and interesting subject of discussion in the post
>
> "Bug in pattern test, or I did something wrong?"
>
>
> I could trace back the problem to an issue with ModuleQ.
>
> Question: Why does
>
> In[12]:= ModuleQ[{0,1,2},expr_]
>
> Out[12]:= True
>
> evaluate to True?
>
>
> My argumentation is as follows:
>
> On the one hand there could be a chance that expr_ is 0,1 or 2 but on 
> the other
> hand the probability that expr_ is not 0,1 or 2 is even higher. As a 
> conclusion it should neither
> evaluate to True nor to False.
>
> In other words: Is there any reason why the expression of everything 
> (named expr)
> is contained in the set {0,1,2} ?
>
> Best,
>
> Christoph




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