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Disjunctive syllogism, also known as Modus Tollendo Tollens is a rule of inference of Propositional logic that states that if P or Q is true and not P is true, then Q is true.

In standard rule form:

$\frac{P \or Q, \neg P}{\therefore Q}$

In sequent notation:

$P \or Q, \neg P \vdash Q$

It is the valid argument form: P or Q. Not P. Therefore, Q.

Natural Deduction Transformation Rules
Rules of inference
Rules of Transformation