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# contrapositive

Given an implication of the form

$p\implies q$ |

(“p implies q”) the *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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new question: difference of a function and a finite sum by pfb