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Timeline for Quadratic Farkas' Lemma?

Current License: CC BY-SA 3.0

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Nov 7, 2012 at 8:25 vote accept Seva
Nov 6, 2012 at 22:42 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 21:17 history edited Seva CC BY-SA 3.0
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Nov 6, 2012 at 21:16 comment added Seva It does seem to work for a pentagon - thanks for the nice example!
Nov 6, 2012 at 20:14 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 20:12 comment added Markus Schweighofer I am so sorry, you are again right. But if you take a pentagon instead of a square, then it works. Not all of the $L_i L_j$ were strictly positive on at least one of the vertices of the square but for the pentagon this works.
Nov 6, 2012 at 20:06 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 17:59 comment added Seva $L_1=1-x$, $L_2=1+x$, $L_3=1-y$, $L_4=1+y$, and $P=2-x^2-y^2$ is not a counterexample in view of $P=L_1L_2+L_3L_4$.
Nov 6, 2012 at 14:50 comment added Markus Schweighofer You are right, I am sorry for suggesting this counterexample. However, I think that I have now a valid counterexample, see above.
Nov 6, 2012 at 14:48 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 7:29 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 7:10 comment added Seva $L_1=1+x$, $L_2=1-x$, and $P=x^2$ is not a counterexample: take all $c_i$ and $c_{ij}$ to be equal to $0$. Many thanks for the references!
Nov 6, 2012 at 7:00 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 4:16 history edited Markus Schweighofer CC BY-SA 3.0
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Nov 6, 2012 at 4:11 history answered Markus Schweighofer CC BY-SA 3.0