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Lemma: It is true that something can be (either) true or false
If \(x\) is a proposition, then the disjunction \(x\vee \neg x\) is a tautology (i.e. always valid).
Examples:
\(\text{"Socrates is a philosopher or Socrates is not a philosopher"}\) is valid.
\(a=2\vee a \neq 2\) is valid.
Table of Contents
Proofs: 1
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