A formula of the language of propositional calculus taking the truth value "true" independently of the truth values "true" or "false" taken by its propositional variables. Examples: $A\supset A$, $A\lor\neg A$, $(A\supset B)\supset(\neg B\supset\neg A)$.
In general one can check whether a given propositional formula is a tautology by simply examining the finite set of all combinations of values of its propositional variables.
|[a1]||Yu.I. Manin, "A course in mathematical logic" , Springer (1977) pp. 31, 54 (Translated from Russian)|
Tautology. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Tautology&oldid=32584