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MathGroup Archive 2007

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Logical Expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73385] Logical Expression
  • From: Martin Schoenecker <ms_usenet at gmx.de>
  • Date: Thu, 15 Feb 2007 04:56:44 -0500 (EST)
  • Organization: Technische Universitaet Darmstadt

Common sense tells me that the statement that "something is equal to
zero, and unequal to zero at the same time" is a false statement:

In[1]:= a == 0 && a != 0
Out[1]= a\[Equal]0&&a=E2=89=A00

In[2]:= LogicalExpand[%]
Out[2]= False

The same, in my opinion, applies to "something is equal to zero and
greater than zero at the same time".  Why doesn't Mathematica think so,
and how to convince it to evaluate the following?

In[3]:= a == 0 && a > 0
Out[3]= a\[Equal]0&&a>0

In[4]:= LogicalExpand[%]
Out[4]= a\[Equal]0&&a>0


Thanks in advance,
Martin


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