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Dec 20, 2014 at 21:16 comment added Turbo I do not really see how it works for dual forms $$f(x_1,\dots,x_{20})=x_1x_2x_3x_4x_5- x_6x_7x_8x_9x_{10}+x_{11}x_{12}x_{13}x_{14}x_{15}-x_{16}x_{17}x_{18}x_{19}x_{20}\in\Bbb R[x].$$
Dec 17, 2014 at 0:33 vote accept Turbo
Dec 17, 2014 at 1:10
Dec 17, 2014 at 0:17 comment added Turbo Interesting.... let me read the article.
Dec 16, 2014 at 22:54 history edited Gjergji Zaimi CC BY-SA 3.0
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Dec 16, 2014 at 22:30 comment added Gjergji Zaimi @Turbo it works for any product of linear forms. This is essentially the argument Alon used to prove the Komjath conjecture about covering the hypercube with hyperplanes.
Dec 16, 2014 at 21:51 comment added Turbo Would the idea work if we had $(x_1+x_2-x_3+x_4)(x_5-x_6-x_7-x_8)(x_9+x_{10}-x_{11}-x_{12})(x_{13}-x_{14}+x_{15}+x_{16})$ (some terms have negative sign)?
Dec 16, 2014 at 6:45 comment added Turbo Yeah you seem correct. My understanding was that $|S|\leq 3$ comes from the fact that $f=0$ if $3$ or less variables are set. It seems the same idea will work for both polynomials(for the first polynomial you can take $|S|\leq 5$ and for the second you can take $|S|\leq3$). But could you clarify the induction step further?
Dec 16, 2014 at 6:37 comment added Gjergji Zaimi The proof would work the same way for all such polynomials. Try to work out an example by hand, the argument is much simpler than my notation makes it seem.
Dec 16, 2014 at 6:23 comment added Turbo Also the proof may not work if we had $$f(x_1,\dots,x_{24})=(x_1+x_2+x_3+x_4)(x_5+x_6+x_7+x_8)(x_9+x_{10}+x_{11}+x_{12})(x_{13}+x_{14}+x_{15}+x_{16})(x_{17}+x_{19}+x_{19}+x_{20})(x_{21}+x_{22}+x_{23}+x_{24})\in\Bbb R[x]$$ or $$f(x_1,\dots,x_{24})=(x_1+x_2+x_3+x_4+x_5+x_6)(x_7+x_8+x_9+x_{10}+x_{11}+x_{12})(x_{13}+x_{14}+x_{15}+x_{16}+x_{17}+x_{18})(x_{19}+x_{20}+x_{21}+x_{22}+x_{23}+x_{24})\in\Bbb R[x]$$ correct?
Dec 16, 2014 at 5:15 history answered Gjergji Zaimi CC BY-SA 3.0