# Proof by contraposition

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**Proof by contraposition**as edited by DavidB4-bot (Talk | contribs) at 17:11, August 25, 2016. This URL is a permanent link to this version of this page.**Proof by Contraposition** is an indirect mathematical proof for a conditional sentence P=>Q that relies upon the tautology (P=>Q)<=>(~Q=>~P).

## Proof by Contraposition of a Conditional Sentence P=>Q

- Assume ~Q.
- ...
- Therefore, ~P.
- Thus, ~Q=>~P
- Therefore, P=>Q