# Logical law

From Encyclopedia of Mathematics

*in mathematical logic*

A logical formula that becomes a true proposition under any interpretation of the variables for propositions and predicates that occur in it. Such formulas are called generally valid, universally valid or tautologies. For example, the tautology $A\lor\neg A$ expresses the law of the excluded middle.

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#### References

[a1] | A. Grzegorczyk, "An outline of mathematical logic" , Reidel (1974) |

**How to Cite This Entry:**

Logical law.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Logical_law&oldid=31440

This article was adapted from an original article by V.E. Plisko (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article