2015/12/03 by Falgas-Ravry, Victor, Zhao, Yi
#05C65 #05C70 #05D99 #Combinatorics (math.CO) #FOS: Mathematics
paper · doi:10.48550/arxiv.1512.01144
Given two 3-uniform hypergraphs F and G, we say that G has an F-covering if we can cover V(G) by copies of F. The minimum codegree of G is the largest integer d such that every pair of vertices from V(G) is contained in at least d triples from E(G). Define c2(n,F) to be the largest minimum codegree among all n-vertex 3-graphs G that contain no F-covering. This is a natural problem intermediate (but distinct) from the well-studied Turán problems and tiling problems. In this paper, we determine c2(n, K4) (for n>98) and the associated extremal configurations (for n>998), where K4 denotes the complete 3-graph on 4 vertices. We also obtain bounds on c2(n,F) which are apart by at most 2 in the cases where F is K4- (K4 with one edge removed), K5-, and the tight cycle C5 on 5 vertices.