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Hardness results for approximate pure Horn CNF formulae minimization

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Abstract

We study the hardness of approximation of clause minimum and literal minimum representations of pure Horn functions in n Boolean variables. We show that unless P=NP, it is not possible to approximate in polynomial time the minimum number of clauses and the minimum number of literals of pure Horn CNF representations to within a factor of \(2^{\log^{1-o(1)} n}\). This is the case even when the inputs are restricted to pure Horn 3-CNFs with O(n 1+ε) clauses, for some small positive constant ε. Furthermore, we show that even allowing sub-exponential time computation, it is still not possible to obtain constant factor approximations for such problems unless the Exponential Time Hypothesis turns out to be false.

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Correspondence to Aritanan Gruber.

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The authors gratefully acknowledge the partial support by NSF grants IIS 0803444 and by CMMI 0856663. The second author also gratefully acknowledge the partial support by the joint CAPES (Brazil)/Fulbright (USA) fellowship process BEX-2387050/15061676.

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Boros, E., Gruber, A. Hardness results for approximate pure Horn CNF formulae minimization. Ann Math Artif Intell 71, 327–363 (2014). https://doi.org/10.1007/s10472-014-9415-9

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