منابع مشابه
Minimal Covers of Formal Languages
Let L1; L2 be languages. If L1 L2, then we say that L2 covers L1. Let C;D be classes of languages over . We call a cover L2 2 C of L1 a C-minimal cover with respect to D if, for all L0 2 C, L1 L0 L2 implies L2 L0 2 D. We examine in detail the particular cases of minimal regular covers and minimal context-free covers, both with respect to nite languages. The closure properties of the class of la...
متن کاملMinimal Covers and Arithmetical Sets1
If a and b are degrees of unsolvability, a is called a minimal cover of b if b<a and no degree c satisfies b<c<a. The degree a is called a minimal cover if it is a minimal cover of some degree b. We prove by a very simple argument that 0" is not a minimal cover for any n. From this result and the axiom of Borel determinateness (BD) we show that the degrees of arithmetical sets (with their usual...
متن کاملMINIMAL COVERS AND HYPERDEGREESf 1 )
Every hyperdegree at or above that of Kleene's O is the hyperjump and the supremum of two minimal hyperdegrees (Theorem 3.1). There is a nonempty ~ZX class of number-theoretic predicates each of which has minimal hyperdegree (Theorem 4.7). If V = L or a generic extension of L, then there are arbitrarily large hyperdegrees which are not minimal over any hyperdegree (Theorems 5.1, 5.2). If <?# ex...
متن کاملOn the dimension of the minimal vertex covers semigroup ring of an unmixed bipartite graph
In a paper in 2008, Herzog, Hibi and Ohsugi introduced and studied the semigroup ring associated to the set of minimal vertex covers of an unmixed bipartite graph. In this paper we relate the dimension of this semigroup ring to the rank of the Boolean lattice associated to the graph.
متن کاملMinimal vertex covers of random trees
We study minimal vertex covers of trees. Contrarily to the number Nvc(A) of minimal vertex covers of the tree A, log Nvc(A) is a self-averaging quantity. We show that, for large sizes n, limn→+∞ < log Nvc(A) >n /n = 0.1033252 ± 10−7. The basic idea is, given a tree, to concentrate on its degenerate vertices, that is those vertices which belong to some minimal vertex cover but not to all of them...
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ژورنال
عنوان ژورنال: Combinatorica
سال: 2017
ISSN: 0209-9683,1439-6912
DOI: 10.1007/s00493-017-3559-2