Q.E.D.
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Q.E.D. is an initialism of the Latin phrase quod erat demonstrandum, meaning "that which was to be demonstrated". Literally, it states "what was to be shown". Traditionally, the abbreviation is placed
Spinoza's original text of Ethics, Part 1, Q.E.D. is used at the end of Demonstratio of Propositio III on the right hand page
Reductio ad absurdum
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In logic, reductio ad absurdum, also known as argumentum ad absurdum, apagogical argument, or proof by contradiction, is the form of argument that attempts to establish a claim by showing that followi
Q.E.D.
…Ipso facto Q.E.A. List of Latin phrases (E) § ergo…
Reductio ad absurdum, painting by John Pettie exhibited at the Royal Academy in 1884