‎Let $n$ be any positive integer‎, ‎the friendship graph $F_n$ consists of $n$ edge-disjoint triangles that all of them meeting in one vertex‎. ‎A graph $G$ is called cospectral with a graph $H$ if their adjacency matrices ...

For a given hypergraph $H$ with chromatic number $chi(H)$ and with no edge containing only one vertex‎, ‎it is shown that the minimum number $l$‎ ‎for which there exists a partition (also a covering) ${E_1,E_2,ldots,E_l}$ ...

A kernel $J$ of a digraph $D$ is an independent set of vertices of $D$ such that for every vertex $w,in,V(D),setminus,J$ there exists an arc from $w$ to a vertex in $J.$‎ ‎In this paper‎, ‎among other results‎, ‎a ...

‎Let $G$ be an $(n,m)$-graph‎. ‎We say that $G$ has property $(ast)$‎ ‎if for every pair of its adjacent vertices $x$ and $y$‎, ‎there ‎exists a vertex $z$‎, ‎such that $z$ is not adjacent‎ ‎to either $x$ or $y$‎. ‎If the ...