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MathGroup Archive 2005

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Re: ! operator

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55932] Re: ! operator
  • From: dh <dh at metrohm.ch>
  • Date: Sun, 10 Apr 2005 23:07:08 -0400 (EDT)
  • References: <d3b18l$sgd$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

DongGook
"!" has two meainings as a prefix operator (and even an additional one 
as a postfix),namely the Not and the Pipe operator. Now Matematica has 
to decide what you mean. If "!" is the first character on a new line, 
Mathematica interpretes "!" as the Pipe character. On the other hand, if 
you write e.g.:
t=!MemeberQ...
Mathematica interpretes "!" as the Not operator.
Sincerely, Daniel

DongGook Park wrote:
> Hi,
> 
> Could you explain a mysterious behaviour of "! operator" as shown below?
> 
> 
> In[43]:=
> MemberQ[{1,2,3},3]
> 
> Out[43]=
> True
> 
> In[47]:=
> !MemberQ[{1,2,3},3]
> (*  Here Mathematica does not give any response!  *)
> 
> In[48]:=
> Not@MemberQ[{1,2,3},3]
> 
> Out[48]=
> False
> 
> 
> Considering the description from Mathematica help:
> 	"!expr is the logical NOT function. It gives False if expr is True,
> and True if it is False."
> This behaviour seems quite suspicious?
> 
> 
> DongGook
> 
> 
> ---------------------------------- 
> DongGook Park, 
> School of Information Technology, 
> SunChon University, Korea 
> Telephone:  +82 61 750 3597 
> Mobile:  +82 18 732 2125 
> Home page:  http://www.dgpark6.com/
> Email:  dgpark6 at sunchon.ac.kr
> 
> 


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