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Re: Negation of Negation wanted

• To: mathgroup at smc.vnet.net
• Subject: [mg44039] Re: Negation of Negation wanted
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Sun, 19 Oct 2003 01:10:33 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

On Saturday, October 18, 2003, at 04:12 PM, Thomas Gutzler wrote:

> Hi,
>
> Assuming f(x) = x1 && x2
>
> Is there a way to get !f(!x), which is:
> !(!x1 && !x2) = x1 || x2
> without copy&paste and manually change it?
>
> Cheers,
>    Tom
>
>
>


  Since you are not using Mathematica syntax (or any other syntax known 
to me) it is not entirely clear what you mean. However, assuming that 
you define your f by

f[x_,y_]:=Not[x]&&Not[y]

you can use LogicalExpand to get:

LogicalExpand[Not[f[Not[a],Not[b]]]]

!a||!b


Andrzej Kozlowski
Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/
http://platon.c.u-tokyo.ac.jp/andrzej/