A new type of decomposition of graphs – the operator decomposition connected with the classical notion of homogeneous set (or module) is introduced. The properties of this decomposition are described. Using this decomposition we prove the following. Let P and Q be two hereditary graph classes such that P is closed with respect to the operation of join and Q is closed with respect to the operati...

A modified k-deck of a graph G is obtained by removing k edges of G in all possible ways, and adding k (not necessarily new) edges in all possible ways. Krasikov and Roditty asked if it was possible to construct the usual k-edge deck of a graph from its modified k-deck. Earlier I solved this problem for the case when k = 1. In this paper, the problem is completely solved for arbitrary k. The pr...

A modified k-deck of a graph is obtained by removing k edges in all possible ways and adding k (not necessarily new) edges in all possible ways. Krasikov and Roditty used these decks to give an independent proof of Müller’s result on the edge reconstructibility of graphs. They asked if a k-edge deck could be constructed from its modified k-deck. In this paper, we solve the problem when k = 1. W...

A graph is said to be reconstructible if it is determined up to isomorphism from the collection of all its one-vertex deleted unlabeled subgraphs. The Reconstruction Conjecture (RC) asserts that all graphs on at least three vertices are reconstructible. In this paper, we prove that all triangle-free graphs G with connectivity two such that diam(G) = 2 or diam(G) = diam(G) = 3 are reconstructibl...

In this paper we de2ne 2ve families of simple graphs {fi,f2,f^,t^ and F=5) such that the reconstruction conjecture is true if reconstruction is proved for either the families $[,$2 & % or the families F=3;F=4 and F=5. These families are quite restrictive in that each has diameter two or three. Then we prove that families F=1;F=2;F=3;F=4 and F=5 are recognizable by proving that graphs of diamete...

We show that the three body Calogero model with inverse square potentials can be interpreted as a maximally superintegrable and multiseparable system in Euclidean three-space. As such it is a special case of a family of systems involving one arbitrary function of one

Motivated by the well-known conjecture by Lovász [6] on the connectivity after the path removal, we study the following problem: There exists a function f = f(k, l) such that the following holds. For every f(k, l)connected graph G and two distinct vertices s and t in G, there are k internally disjoint paths P1, . . . , Pk with endpoints s and t such that G− ⋃k i=1 V (Pi) is l-connected. When k ...

We formulate a reconstruction problem for functions of several arguments: Is a function of several arguments uniquely determined, up to equivalence, by its identification minors? We establish some positive and negative results on this reconstruction problem. In particular, we show that totally symmetric functions (of sufficiently large arity) are reconstructible.

‎In this paper‎, ‎we investigate the number of 1-factors of a‎ ‎generalized Petersen graph $P(N,k)$ and get a lower bound for the‎ ‎number of 1-factors of $P(N,k)$ as $k$ is odd‎, ‎which shows that the‎ ‎number of 1-factors of $P(N,k)$ is exponential in this case and‎ ‎confirms a conjecture due to Lovász and Plummer (Ann‎. ‎New York Acad‎. ‎Sci‎. ‎576(2006)‎, ‎no‎. ‎1‎, ‎389-398).

For a finite group $G$‎, ‎let $Cent(G)$ denote the set of centralizers of single elements of $G$‎. ‎In this note we prove that if $|G|leq frac{3}{2}|Cent(G)|$ and $G$ is 2-nilpotent‎, ‎then $Gcong S_3‎, ‎D_{10}$ or $S_3times S_3$‎. ‎This result gives a partial and positive answer to a conjecture raised by A‎. ‎R‎. ‎Ashrafi [On finite groups with a given number of centralizers‎, ‎Algebra‎ ‎Collo...