Abstract. We study the relationship between the sizes of sets B, S in R n where B contains the k-skeleton of an axes-parallel cube around each point in S, generalizing the results of Keleti, Nagy, and Shmerkin [6] about such sets in the plane. We find sharp estimates for the possible packing and boxcounting dimensions for B and S. These estimates follow from related cardinality bounds for sets containing the discrete skeleta of cubes around a finite set of a given size. The Katona-Kruskal Theorem from hypergraph theory plays an important role. We also find partial results for the Haussdorff dimension and settle an analogous question for the dual polytope of the cube, the orthoplex.
Introduction and Statements of Results
1.1.Introduction. In [6] the authors find sharp bounds for the Hausdorff, boxcounting, and packing dimensions of sets S, B ⊆ R 2 where B contains either the vertices or boundary of an axes-parallel square around every point in S, and cardinality bounds for finite sets satisfying discrete versions of these conditions. Their results are summarized in the following table. If S has size s for the given notion of size, then a sharp lower bound for the size of B is given in terms of s:
Notion of SizeVertex problem Boundary problem (0-skeleton of a 2-cube) (1-skeleton of a 2-cube)