03B05-Contrapositive.tex

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Given an implication of the form
$$p \implies q$$
(``p implies q'') the \emph{contrapositive} of this implication is
$$\neg q \implies \neg p$$
(``not q implies not p'').

An implication and its contrapositive are equivalent statements.  When proving a theorem, it is often more convenient or more intuitive to prove the contrapositive instead.
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