منابع مشابه
Information Hiding by Coverings *
We propose a formal model for embedding information in black-white images and prove the equivalence between existence of embedding schemes and covering codes. An asymptoticly tight bound on the performance of embedding schemes is given. We construct efficient embedding schemes via known coverings. In particular, one of those schemes allows to embed up to log 2 (n + 1) bits in coverwords of n bi...
متن کاملTolerances Induced by Irredundant Coverings
In this paper, we consider tolerances induced by irredundant coverings. Each tolerance R on U determines a quasiorder .R by setting x .R y if and only if R(x) ⊆ R(y). We prove that for a tolerance R induced by a covering H of U , the covering H is irredundant if and only if the quasiordered set (U,.R) is bounded by minimal elements and the tolerance R coincides with the product &R ◦.R. We also ...
متن کاملMultiple vertex coverings by cliques
For positive integers m1, . . . ,mk, let f(m1, . . . ,mk) be the minimum order of a graph whose edges can be coloured with k colours such that every vertex is in a clique of cardinality mi all of whose edges have the i th colour for all i = 1, 2, . . . , k. The value for k = 2 was determined by Entringer et al. (J. Graph Theory 24 (1997), 21–23). We show that if k is fixed then f(m, . . . ,m) =...
متن کاملBranched Coverings Defined by Triangulations
A canonical branched covering over each sufficiently good simplicial complex is constructed. Its structure depends on the combinatorial type of the complex. In this way, each closed orientable 3-manifold arises as a branched covering over S3 from some triangulation of S3. This result is related to a theorem of Hilden [9] and Montesinos [16]. The branched coverings introduced admit a rich theory...
متن کاملm-Level rook placements
Goldman, Joichi, and White proved a beautiful theorem showing that the falling factorial generating function for the rook numbers of a Ferrers board factors over the integers. Briggs and Remmel studied an analogue of rook placements where rows are replaced by sets of m rows called levels. They proved a version of the factorization theorem in that setting, but only for certain Ferrers boards. We...
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ژورنال
عنوان ژورنال: Journal of Combinatorial Theory
سال: 1970
ISSN: 0021-9800
DOI: 10.1016/s0021-9800(70)80018-7