Timeline for Techniques for showing non-derivability in logics and other formal proof systems

9 events

when toggle format	what		by	license	comment
Apr 21, 2012 at 9:50	vote	accept	Dave Clarke
Oct 26, 2010 at 20:15	comment	added	Kaveh		Thanks for the clarification, my mind goes to first-order logic by default when I read classical logic. :)
Oct 26, 2010 at 19:59	comment	added	Dave Clarke		I changed it to classical propositional logic. The question asks for any technique apart from proving the negation, as many formal system (collections of axioms and inference rules) do not have negation, or in fact may not even look like "logic".
Oct 26, 2010 at 19:58	history	edited	Dave Clarke	CC BY-SA 2.5	added 65 characters in body; edited title
Oct 26, 2010 at 19:48	comment	added	Kaveh		Dave, I think there is a typo in the question, to show that $\varphi$ is not derivable we don't show that $\lnot \varphi$ is derivable, we just show that it is consistent, and this is only based on consistency of classical logic. If the logic is first-order classical logic, then there are sentences that we can neither prove nor refute (unless we are talking about a complete theory). Or am I misreading your question?
Oct 26, 2010 at 15:10	history	edited	Dave Clarke	CC BY-SA 2.5	edited title
Oct 26, 2010 at 14:48	history	edited	Dave Clarke	CC BY-SA 2.5	added 184 characters in body
Oct 26, 2010 at 14:41	answer	added	Neel Krishnaswami		timeline score: 15
Oct 26, 2010 at 12:51	history	asked	Dave Clarke	CC BY-SA 2.5