On the number of cut-vertices in a graph.
A cut-vertex in a graph G is a vertex whose removal increases the number of connected components of G. An end-block of G is a block with a single cut-vertex. In this paper we establish upper bounds on the numbers of end-blocks and cut-vertices in a 4-regular graph G and claw-free 4-regular graphs. We characterize the extremal graphs achieving these bounds.
A property P defined on all graphs of order n is said to be k-stable if for any graph of order n that does not satisfy P, the fact that uv is not an edge of G and that G + uv satisfies P implies . Every property is (2n-3)-stable and every k-stable property is (k+1)-stable. We denote by s(P) the smallest integer k such that P is k-stable and call it the stability of P. This number usually depends on n and is at most 2n-3. A graph of order n is said to be pancyclic if it contains cycles of all lengths...
In this paper we initiate the study of total restrained domination in graphs. Let be a graph. A total restrained dominating set is a set where every vertex in is adjacent to a vertex in as well as to another vertex in , and every vertex in is adjacent to another vertex in . The total restrained domination number of , denoted by , is the smallest cardinality of a total restrained dominating set of . First, some exact values and sharp bounds for are given in Section 2. Then the Nordhaus-Gaddum-type...
A graph G is called (H;k)-vertex stable if G contains a subgraph isomorphic to H ever after removing any of its k vertices. Q(H;k) denotes the minimum size among the sizes of all (H;k)-vertex stable graphs. In this paper we complete the characterization of -vertex stable graphs with minimum size. Namely, we prove that for m ≥ 2 and n ≥ m+2, and as well as are the only -vertex stable graphs with minimum size, confirming the conjecture of Dudek and Zwonek.
The reverse Wiener index of a connected graph is defined as where is the number of vertices, is the diameter, and is the Wiener index (the sum of distances between all unordered pairs of vertices) of . We determine the -vertex non-starlike trees with the first four largest reverse Wiener indices for , and the -vertex non-starlike non-caterpillar trees with the first four largest reverse Wiener indices for .