$T$-preserving homomorphisms of oriented graphs

Jaroslav Nešetřil; Eric Sopena; Laurence Vignal

Displaying similar documents to “$T$-preserving homomorphisms of oriented graphs”

Set colorings in perfect graphs

Ralucca Gera, Futaba Okamoto, Craig Rasmussen, Ping Zhang (2011)

Mathematica Bohemica

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For a nontrivial connected graph $G$ , let $c : V (G) \to ℕ$ be a vertex coloring of $G$ where adjacent vertices may be colored the same. For a vertex $v \in V (G)$ , the neighborhood color set $NC (v)$ is the set of colors of the neighbors of $v$ . The coloring $c$ is called a set coloring if $NC (u) \neq NC (v)$ for every pair $u, v$ of adjacent vertices of $G$ . The minimum number of colors required of such a coloring is called the set chromatic number $χ_{s} (G)$ . We show that the decision variant of determining $χ_{s} (G)$ is NP-complete in the general case, and show that...

On integral sum graphs with a saturated vertex

Zhibo Chen (2010)

Czechoslovak Mathematical Journal

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As introduced by F. Harary in 1994, a graph $G$ is said to be an $i n t e g r a l$ $s u m$ $g r a p h$ if its vertices can be given a labeling $f$ with distinct integers so that for any two distinct vertices $u$ and $v$ of $G$ , $u v$ is an edge of $G$ if and only if $f (u) + f (v) = f (w)$ for some vertex $w$ in $G$ . We prove that every integral sum graph with a saturated vertex, except the complete graph $K_{3}$ , has edge-chromatic number equal to its maximum degree. (A vertex of a graph $G$ is said to be if it is adjacent to every...

Set vertex colorings and joins of graphs

Futaba Okamoto, Craig W. Rasmussen, Ping Zhang (2009)

Czechoslovak Mathematical Journal

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For a nontrivial connected graph $G$ , let $c V (G) \to ℕ$ be a vertex coloring of $G$ where adjacent vertices may be colored the same. For a vertex $v$ of $G$ , the neighborhood color set $NC (v)$ is the set of colors of the neighbors of $v$ . The coloring $c$ is called a set coloring if $NC (u) \neq NC (v)$ for every pair $u, v$ of adjacent vertices of $G$ . The minimum number of colors required of such a coloring is called the set chromatic number $χ_{s} (G)$ . A study is made of the set chromatic number of the join $G + H$ of two graphs $G$ and $H$ . Sharp lower...