Notebooks 06 Aug 2002 17:30 A much-abused result in mathematical logic consistent if, given the axioms and the derivation rules, we can never derive two contradictory propositions; obviously, we want our axiomatic systems to be consistent. (The trick is to replace each symbol in the proposition, including numerals, either the system is inconsistent (horrors!), or incomplete, and the truth of those propositions is undecidable (within that system). Such undecidable propositions are known as or models of Peano arithmetic.) It follows that these systems, too, contain undecidable propositions, and are incomplete. deduction from axioms, all arithmetical propositions. And that is all. quod erat demonstrandum. This would actually be a valid demonstration, were only the pentultimate sentence true; but no one has ever presented any evidence that it is true, only vigorous hand-waving and the occasional heartfelt assertion. (Thanks to Jakub Jasinski for politely pointing out an embarrassing error in an earlier version.) Recommended: - Michael Arbib
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