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MathGroup Archive 2005

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Re: ((a&&b)||c)==((a||c)&&(b||c))

  • To: mathgroup at
  • Subject: [mg62057] Re: [mg62015] ((a&&b)||c)==((a||c)&&(b||c))
  • From: "Steven T. Hatton" <hattons at>
  • Date: Thu, 10 Nov 2005 02:50:43 -0500 (EST)
  • References: <> <> <>
  • Sender: owner-wri-mathgroup at

Andrzej Kozlowski wrote:

> On 9 Nov 2005, at 17:45, Steven T. Hatton wrote:
>> Why does Mathematica not determine that the following is true?
>> ((a \[And] b) \[Or] c) == ((a \[Or] c) \[And] (b \[Or] c))

> Because, (as I tried to explain in a reply to a recent posting of
> yours) this is not the way == is used in Mathematica. The correct way
> to show this is:

The rules of logic are very tricky.  For example:

Tautology <=> True
P && Tautology <=> P
P || Tautology <=> Tautology
!Tautology <=> Contradiction

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