the proof you abridged is an internet joke that can be found at http://boston.craigslist.org/about/best/nyc/13167841.html
in Usenet groups, the joke ends with "since evil is negative, the square root of evil must be imaginary, which would mean that money is imaginary, and therefore, time must also be imaginary."
if p then q (statement)
if p then not q (negation)
if q then p (converse)
if not p then not q (inverse)
if not q then not p (contrapositive)
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