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arXiv · 1605.00723

Solving and Verifying the boolean Pythagorean Triples problem via Cube-and-Conquer

Marijn J. H. Heule·Oliver Kullmann·Victor W. Marek
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Abstract

The boolean Pythagorean Triples problem has been a longstanding open problem in Ramsey Theory: Can the set N = $\{1, 2, ...\}$ of natural numbers be divided into two parts, such that no part contains a triple $(a,b,c)$ with $a^2 + b^2 = c^2$ ? A prize for the solution was offered by Ronald Graham over two decades ago. We solve this problem, proving in fact the impossibility, by using the Cube-and-Conquer paradigm, a hybrid SAT method for hard problems, employing both look-ahead and CDCL solvers. An important role is played by dedicated look-ahead heuristics, which indeed allowed to solve the problem on a cluster with 800 cores in about 2 days. Due to the general interest in this mathematical problem, our result requires a formal proof. Exploiting recent progress in unsatisfiability proofs of SAT solvers, we produced and verified a proof in the DRAT format, which is almost 200 terabytes in size. From this we extracted and made available a compressed certificate of 68 gigabytes, that allows anyone to reconstruct the DRAT proof for checking.

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Marijn J. H. Heule, Oliver Kullmann, Victor W. Marek. 2016-05-03. Solving and Verifying the boolean Pythagorean Triples problem via Cube-and-Conquer. https://doi.org/10.1007/978-3-319-40970-2_15

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