A note on two comparability graphs
A note on two multicolor Ramsey numbers.
A note on ultrametric matrices
It is proved in this paper that special generalized ultrametric and special matrices are, in a sense, extremal matrices in the boundary of the set of generalized ultrametric and matrices, respectively. Moreover, we present a new class of inverse -matrices which generalizes the class of matrices.
A Note on Uniquely Embeddable Forests
Let F be a forest of order n. It is well known that if F 6= Sn, a star of order n, then there exists an embedding of F into its complement F. In this note we consider a problem concerning the uniqueness of such an embedding.
A note on uniquely embeddable graphs
Let G be a simple graph of order n and size e(G). It is well known that if e(G) ≤ n-2, then there is an embedding G into its complement [G̅]. In this note, we consider a problem concerning the uniqueness of such an embedding.
A note on uniquely H-colourable graphs
For a graph H, we compare two notions of uniquely H-colourable graphs, where one is defined via automorphisms, the second by vertex partitions. We prove that the two notions of uniquely H-colourable are not identical for all H, and we give a condition for when they are identical. The condition is related to the first homomorphism theorem from algebra.
A note on upper bound for chromatic number of a graph.
A note on upper embeddable graphs
A Note On Vertex Colorings Of Plane Graphs
Given an integer valued weighting of all elements of a 2-connected plane graph G with vertex set V , let c(v) denote the sum of the weight of v ∈ V and of the weights of all edges and all faces incident with v. This vertex coloring of G is proper provided that c(u) ≠ c(v) for any two adjacent vertices u and v of G. We show that for every 2-connected plane graph there is such a proper vertex coloring with weights in {1, 2, 3}. In a special case, the value 3 is improved to 2.
A note to independent sets in scheduling
The paper studies the bus-journey graphs in the case when they are piecewise expanding and contracting (if described by fathers-sons relations starting with the greatest independent set of nodes). This approach can make it possible to solve the minimization problem of the total service time of crews.
A numerical invariant for finitely generated groups via actions on graphs.
A -analogue of a formula of Frobenius.
A paintability version of the combinatorial Nullstellensatz, and list colorings of -partite -uniform hypergraphs.
A parallelogram configuration condition in nets
After describing a (general and special) coordinatization of -nets there are found algebraic equivalents for the validity of certain quadrangle configuration conditions in -nets with small degree .
A parametric analysis of the largest induced tree problem in random graphs
A parametrization of the abstract Ramsey theorem.
A partition identity with certain applications
A partition of connected graphs.
A partition of R in two homogeneous and homeomorphic parts
A partition of the Catalan numbers and enumeration of genealogical trees
A special relational structure, called genealogical tree, is introduced; its social interpretation and geometrical realizations are discussed. The numbers of all abstract genealogical trees with exactly n+1 nodes and k leaves is found by means of enumeration of code words. For each n, the form a partition of the n-th Catalan numer Cₙ, that means .