For every proposition involving logical addition and multiplication ("or" and "and"), there is a corresponding proposition in which the words "addition" and "multiplication" are interchanged.
de Morgan's Duality Law
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Cite this as:
Weisstein, Eric W. "de Morgan's Duality Law." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/deMorgansDualityLaw.html