For every pair of nite connected graphs F and H, and every integer k, we construct a universal graph U with the following properties: 1. There is a homomorphism : U ! H, but no homomorphism from F to U . 2. For every graph G with maximal degree no more than k having a homomorphism h : G! H, but no homomorphism from F to G, there is a homomorphism : G! U , such that h = . Particularly, this solv...

Time-Delay Interferometry (TDI) is the data processing technique that cancels large laser phase fluctuations affecting one-way Doppler measurements made by unequal-arm space-based gravitational wave interferometers. By taking finite linear combinations of properly time-shifted measurements, are removed at any time $t$ and signals can be studied a requisite level precision. In this article we sh...

The chromatic sum Σ(G) of a graph G is the smallest sum of colors among of proper coloring with the natural number. In this paper, we introduce a necessary condition for the existence of graph homomorphisms. Also, we present Σ(G) < χf (G)|G| for every graph G.

We consider the complexity of oriented homomorphism and two of its variants, namely strong oriented homomorphism and pushable homomorphism, for planar graphs with large girth. In each case, we consider the smallest target graph such that the corresponding homomorphism is NP-complete. These target graphs T4, T5, and T6 have 4, 5, and 6 vertices, respectively. For i ∈ {4, 5, 6} and for every g, w...

We present an algebraic description of tabular parsing algorithms that avoids a significant problem of Sikkel’s description, namely that inconsistent parse items cannot be represented. We show that a parse item must be regarded as a pair consisting of a congruence class of partial parse trees and a tuple of strings. A tabular parsing algorithm is described algebraically by a pair of algebras wi...

Let B be a strictly real commutative real Banach algebra with the carrier space Φ B. If A is a commutative real Banach algebra, then we give a representation of a ring homomorphism ρ : A → B, which needs not be linear nor continuous. If A is a commutative complex Banach algebra, then ρ(A) is contained in the radical of B. 1. Introduction and results. Ring homomorphisms are mappings between two ...

Given a finitely presented group G = 〈X;R〉, the word problem asks to decide effectively whether a given word in the free group w ∈ F (X) represents the identity element in G or not. Another important computational problem is to check effectively whether G is finite or not. For the ”No” parts of these problems, we can use quotient tests. For instance, for the ”No” part of the word problem, we ca...

let $g$ be a finite group. we construct the prime graph of $ g $,which is denoted by $ gamma(g) $ as follows: the vertex set of thisgraph is the prime divisors of $ |g| $ and two distinct vertices $ p$ and $ q $ are joined by an edge if and only if $ g $ contains anelement of order $ pq $.in this paper, we determine finite groups $ g $ with $ gamma(g) =gamma(l_3(q)) $, $2 leq q < 100 $ and prov...

We show that the Green correspondence induces an injective group homomorphism from linear source Picard L(B) of a block B finite algebra to L(C), where C is Brauer correspondent B. This maps trivial T(B) T(C). further endopermutation E(B) bounded in terms defect groups and when has normal E(B)=L(B). Finally we prove rank any invertible B-bimodule by