How is negation of a tautology a tautology? I am reading the book Elements of Discrete Mathematics by C L Liu. On the first chapter about Sets and Propositions, under the heading TAUTOLOGIES the author states > It may be observed that the conjunction of a tautology is also a tautology. **The negation of a tautology is also a tautology.** Screen Grab from the book How is this true? OR It is not true and just a mistake that needs to be corrected?

It is wrong (it must be a typo...).

The negation of a tautology#Definition_and_examples) is a formula that is Always FALSE, i.e. a contradiction.

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_Note_ added June 27.

I've browsed the Second Ed. (1985) of Liu's textbook and I've not found the wrong statement.