Abstract
We show that there is a system of 14 non-trivial finitary functions on the random graph with the following properties: Any non-trivial function on the random graph generates one of the functions of this system by means of composition with automorphisms and by topological closure, and the system is minimal in the sense that no subset of the system has the same property. The theorem is obtained by proving a Ramsey-type theorem for colorings of tuples in finite powers of the random graph, and by applying this to find regular patterns in the behavior of any function on the random graph. As model-theoretic corollaries of our methods we rederive a theorem of Simon Thomas classifying the first-order closed reducts of the random graph, and prove some refinements of this theorem; also, we obtain a classification of the maximal reducts closed under primitive positive definitions, and prove that all reducts of the random graph are model-complete.
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The research leading to these results has received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013 Grant Agreement no. 257039). The second author is grateful for support through Erwin Schrödinger Fellowship J2742-N18 of the Austrian Science Fund and through an APART-fellowship of the Austrian Academy of Sciences.
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Bodirsky, M., Pinsker, M. Minimal functions on the random graph. Isr. J. Math. 200, 251–296 (2014). https://doi.org/10.1007/s11856-014-1042-y
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DOI: https://doi.org/10.1007/s11856-014-1042-y