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Re: Logical Expression

• To: mathgroup at smc.vnet.net
• Subject: [mg73415] Re: [mg73385] Logical Expression
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Fri, 16 Feb 2007 00:52:42 -0500 (EST)
• Reply-to: hanlonr at cox.net

Use Simplify

Simplify[a == 0 && a > 0]

False


Bob Hanlon

---- Martin Schoenecker <ms_usenet at gmx.de> wrote: 
> 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