The VC-dimension of a set system is a way to capture its complexity and has been a key parameter studied extensively in machine learning and geometry communities. In this paper, we resolve two longstanding open problems on bounding the VC-dimension of two fundamental set systems: k-fold unions/intersections of half-spaces, and the simplices set system. Among other implications, it settles an open question in machine learning that was first studied in the 1989 foundational paper of Blumer, Ehrenfeucht, Haussler and Warmuth [4] as well as by Eisenstat and Angluin [8] and Johnson [11].

A graph G is H-saturated for a graph H, if G does not contain a copy of H but adding any new edge to G results in such a copy. An H-saturated graph on a given number of vertices always exists and the properties of such graphs, for example their highest density, have been studied intensively.A graph G is H-induced-saturated if G does not have an induced subgraph isomorphic to H, but adding an edge to G from its complement or deleting an edge from G results in an induced copy of H. It is not immediate anymore that H-induced-saturated graphs exist. In fact, Martin and Smith (2012) showed that there is no P 4 -induced-saturated graph. Behrens et al. (2016) proved that if H belongs to a few simple classes of graphs such as a class of odd cycles of length at least 5, stars of size at least 2, or matchings of size at least 2, then there is an H-induced-saturated graph.This paper addresses the existence question for H-induced-saturated graphs. It is shown that Cartesian products of cliques are H-induced-saturated graphs for H in several infinite families, including large families of trees. A complete characterization of all connected graphs H for which a Cartesian product of two cliques is an H-induced-saturated graph is given. Finally, several results on induced saturation for prime graphs and families of graphs are provided.

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