Large Degree Vertices in Longest Cycles of Graphs, I
In this paper, we consider the least integer d such that every longest cycle of a k-connected graph of order n (and of independent number α) contains all vertices of degree at least d.
In this paper, we consider the least integer d such that every longest cycle of a k-connected graph of order n (and of independent number α) contains all vertices of degree at least d.
Let be a path on vertices. In an earlier paper we have proved that each polyhedral map on any compact -manifold with Euler characteristic contains a path such that each vertex of this path has, in , degree . Moreover, this bound is attained for or , even. In this paper we prove that for each odd , this bound is the best possible on infinitely many compact -manifolds, but on infinitely many other compact -manifolds the upper bound can be lowered to .
A collection (1 ≤ t ≤ k) of t disjoint paths, s of them being singletons with |V(L)| = k is called a (k,t,s)-linear forest. A graph G is (k,t,s)-ordered if for every (k,t,s)-linear forest L in G there exists a cycle C in G that contains the paths of L in the designated order as subpaths. If the cycle is also a hamiltonian cycle, then G is said to be (k,t,s)-ordered hamiltonian. We give sharp sum of degree conditions for nonadjacent vertices that imply a graph is (k,t,s)-ordered hamiltonian.
It is shown that every 3-connected planar graph with a large number of vertices has a long induced path.
L-zero-divisor graphs of L-commutative rings have been introduced and studied in [5]. Here we consider L-zero-divisor graphs of a finite direct product of L-commutative rings. Specifically, we look at the preservation, or lack thereof, of the diameter and girth of the L-ziro-divisor graph of a L-ring when extending to a finite direct product of L-commutative rings.