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It is known that the cop number $c(G)$ of a connected graph $G$ can be bounded as a function of the genus of the graph $g(G)$. The best known bound, that $c(G) leq leftlfloor frac{3 g(G)}{2}rightrfloor + 3$, was given by Schr{o}der, who conjectured that in fact $c(G) leq g(G) + 3$. We give the first improvement to Schr{o}ders bound, showing that $c(G) leq frac{4g(G)}{3} + frac{10}{3}$.
We show that the cop number of every generalized Petersen graph is at most 4. The strategy is to play a modified game of cops and robbers on an infinite cyclic covering space where the objective is to capture the robber or force the robber towards an
An oriented graph $G^sigma$ is a digraph without loops or multiple arcs whose underlying graph is $G$. Let $Sleft(G^sigmaright)$ be the skew-adjacency matrix of $G^sigma$ and $alpha(G)$ be the independence number of $G$. The rank of $S(G^sigma)$ is c
We establish a lower bound for the energy of a complex unit gain graph in terms of the matching number of its underlying graph, and characterize all the complex unit gain graphs whose energy reaches this bound.
The $2$-cell embeddings of graphs on closed surfaces have been widely studied. It is well known that ($2$-cell) embedding a given graph $G$ on a closed orientable surface is equivalent to cyclically ordering the edges incident to each vertex of $G$.
In 1982, Zaslavsky introduced the concept of a proper vertex colouring of a signed graph $G$ as a mapping $phicolon V(G)to mathbb{Z}$ such that for any two adjacent vertices $u$ and $v$ the colour $phi(u)$ is different from the colour $sigma(uv)phi(v