We survey problems, results, and methods concerning k-facets and k-sets of finite point sets in real affine d-space and the dual notion of levels in arrangements of hyperplanes.

for every positive integer k, a set s of vertices in a graph g = (v;e) is a k- tuple dominating set of g if every vertex of v -s is adjacent to at least k vertices and every vertex of s is adjacent to at least k - 1 vertices in s. the minimum cardinality of a k-tuple dominating set of g is the k-tuple domination number of g. when k = 1, a k-tuple domination number is the well-studied domination...

In this paper, motivated by the study of the wide diameter and the Rabin number of graphs, we define the generalized k-diameter of k-connected graphs, and show that every k-regular k-connected graph on n vertices has the generalized k-diameter at most n/2 and this upper bound cannot be improved when n = 4k − 6 + i(2k − 4).

The ratio Φ → K + K − /K 0 ¯ K 0 is discussed and its present experimental value is compared with theoretical expectations. A difference larger than two standard deviations is observed. We critically examine a number of mechanisms that could account for this discrepancy, which remains unexplained. Measurements at DAΦNE at the level of the per mille accuracy can clarify whether there exist any a...

A Boolean formula in a conjunctive normal form is called a (k, s)-formula if every clause contains exactly k variables and every variable occurs in at most s clauses. We show that there are unsatisfiable (k, 4 · 2 k