On the representation of abstract semigroups by transformation semigroups : Computer investigations.
On the resilience of long cycles in random graphs.
On the resolvability of Hall triple systems
È ben noto che fra le classi di sistemi ternari di Hall (HTS), gli HTS Abeliani ammettano una risoluzione siccome sono esattamente gli spazi affini finiti d'ordine 3; per questi sistemi una tal risoluzione è fornita dalla relazione di parallelismo. In questa nota viene dimostrato che certe classi di HTS non Abeliani costrutti dai gruppi di Burnside , anche ammettono una risoluzione. Allora, questi esempi di HTS si possono considerare anche come spazi finiti di Sperner e dunque la nota conclude...
On the rooted Tutte polynomial
The Tutte polynomial is a generalization of the chromatic polynomial of graph colorings. Here we present an extension called the rooted Tutte polynomial, which is defined on a graph where one or more vertices are colored with prescribed colors. We establish a number of results pertaining to the rooted Tutte polynomial, including a duality relation in the case that all roots reside around a single face of a planar graph.
On the rules for the elimination of the non-canonical Morgan trees
On the second Laplacian spectral moment of a graph
Kragujevac (M. L. Kragujevac: On the Laplacian energy of a graph, Czech. Math. J. 56(131) (2006), 1207–1213) gave the definition of Laplacian energy of a graph and proved ; equality holds if and only if . In this paper we consider the relation between the Laplacian energy and the chromatic number of a graph and give an upper bound for the Laplacian energy on a connected graph.
On the second largest eigenvalue of a mixed graph
Let G be a mixed graph. We discuss the relation between the second largest eigenvalue λ₂(G) and the second largest degree d₂(G), and present a sufficient condition for λ₂(G) ≥ d₂(G).
On the selection of pairs
On the semigroup of binary relations on a finite set
On the semigroup of fully indecomposable relations
On the sequence A079500 and its combinatorial interpretations.
On the set of all maximal matchings
On the set of all shortest paths of a given length in a connected graph
On the set of distances between two sets over finite fields.
On the Set-Partitioning Problem
On the shadow of squashed families of -sets.
On the sharpness of some results relating cuts and crossing numbers.
On the Signed (Total) K-Independence Number in Graphs
Let G be a graph. A function f : V (G) → {−1, 1} is a signed k- independence function if the sum of its function values over any closed neighborhood is at most k − 1, where k ≥ 2. The signed k-independence number of G is the maximum weight of a signed k-independence function of G. Similarly, the signed total k-independence number of G is the maximum weight of a signed total k-independence function of G. In this paper, we present new bounds on these two parameters which improve some existing bounds....
On the signless Laplacian spectral characterization of the line graphs of -shape trees
A graph is determined by its signless Laplacian spectrum if no other non-isomorphic graph has the same signless Laplacian spectrum (simply is ). Let denote the -shape tree obtained by identifying the end vertices of three paths , and . We prove that its all line graphs except () are , and determine the graphs which have the same signless Laplacian spectrum as . Let be the maximum signless Laplacian eigenvalue of the graph . We give the limit of , too.
On the simplex graph operator
A simplex of a graph G is a subgraph of G which is a complete graph. The simplex graph Simp(G) of G is the graph whose vertex set is the set of all simplices of G and in which two vertices are adjacent if and only if they have a non-empty intersection. The simplex graph operator is the operator which to every graph G assigns its simplex graph Simp(G). The paper studies graphs which are fixed in this operator and gives a partial answer to a problem suggested by E. Prisner.