       Re: Logical Expression

• To: mathgroup at smc.vnet.net
• Subject: [mg73429] Re: Logical Expression
• From: "dimitris" <dimmechan at yahoo.com>
• Date: Fri, 16 Feb 2007 01:00:21 -0500 (EST)
• References: <er1auu\$57j\$1@smc.vnet.net>

```I am not able to explain this behavior of LogicalExpand.
But you can use FullSimplify instead.

a == 0 && a != 0
FullSimplify[%]

a == 0 && a != 0
False

a == 0 && a > 0
FullSimplify[%]

a == 0 && a > 0
False

Dimitris

=CF/=C7 Martin Schoenecker =DD=E3=F1=E1=F8=E5:
> 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:= a == 0 && a != 0
> Out= a\[Equal]0&&a=E2=89=A00
>
> In:= LogicalExpand[%]
> Out= 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:= a == 0 && a > 0
> Out= a\[Equal]0&&a>0
>
> In:= LogicalExpand[%]
> Out= a\[Equal]0&&a>0
>
>