منابع مشابه
Reducts of the generic digraph
The generic digraph (D,E) is the unique countable homogeneous digraph that embeds all finite digraphs. In this paper, we determine the lattice of reducts of (D,E), where a structure M is a reduct of (D,E) if it has domain D and all its ∅-definable relations are ∅-definable relations of (D,E). As (D,E) is א0-categorical, this is equivalent to determining the lattice of closed groups that lie in ...
متن کاملThe Italian domatic number of a digraph
An {em Italian dominating function} on a digraph $D$ with vertex set $V(D)$ is defined as a function$fcolon V(D)to {0, 1, 2}$ such that every vertex $vin V(D)$ with $f(v)=0$ has at least two in-neighborsassigned 1 under $f$ or one in-neighbor $w$ with $f(w)=2$. A set ${f_1,f_2,ldots,f_d}$ of distinctItalian dominating functions on $D$ with the property that $sum_{i=1}^d f_i(v)le 2$ for each $vi...
متن کاملDigraph related constructions and the complexity of digraph homomorphism problems
The role of polymorphisms in determining the complexity of constraint satisfaction problems is well established. In this context we study the stability of CSP complexity and polymorphism properties under some basic graph theoretic constructions. As applications we observe a collapse in the applicability of algorithms for CSPs over directed graphs with both a total source and a total sink: the c...
متن کاملA note on the Roman domatic number of a digraph
Roman dominating function} on a digraph $D$ with vertex set $V(D)$ is a labeling$fcolon V(D)to {0, 1, 2}$such that every vertex with label $0$ has an in-neighbor with label $2$. A set ${f_1,f_2,ldots,f_d}$ ofRoman dominating functions on $D$ with the property that $sum_{i=1}^d f_i(v)le 2$ for each $vin V(D)$,is called a {em Roman dominating family} (of functions) on $D$....
متن کاملDigraph Decompositions and Monotonicity in Digraph Searching
We consider monotonicity problems for graph searching games. Variants of these games – defined by the type of moves allowed for the players – have been found to be closely connected to graph decompositions and associated width measures such as pathor tree-width. Of particular interest is the question whether these games are monotone, i.e. whether the cops can catch a robber without ever allowin...
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ژورنال
عنوان ژورنال: Annals of Pure and Applied Logic
سال: 2016
ISSN: 0168-0072
DOI: 10.1016/j.apal.2015.12.006