Note on a theorem of J. Baumgartner
Note on linear arboricity
Note on linear arboricity
Note on linear arboricity of graphs with large girth
Note On The Game Colouring Number Of Powers Of Graphs
We generalize the methods of Esperet and Zhu [6] providing an upper bound for the game colouring number of squares of graphs to obtain upper bounds for the game colouring number of m-th powers of graphs, m ≥ 3, which rely on the maximum degree and the game colouring number of the underlying graph. Furthermore, we improve these bounds in case the underlying graph is a forest.
Note: Sharp Upper and Lower Bounds on the Number of Spanning Trees in Cartesian Product of Graphs
Let G1 and G2 be simple graphs and let n1 = |V (G1)|, m1 = |E(G1)|, n2 = |V (G2)| and m2 = |E(G2)|. In this paper we derive sharp upper and lower bounds for the number of spanning trees τ in the Cartesian product G1 □G2 of G1 and G2. We show that: [...] and [...] . We also characterize the graphs for which equality holds. As a by-product we derive a formula for the number of spanning trees in Kn1 □Kn2 which turns out to be [...] .
Nowhere-zero modular edge-graceful graphs
For a connected graph G of order n ≥ 3, let f: E(G) → ℤₙ be an edge labeling of G. The vertex labeling f’: V(G) → ℤₙ induced by f is defined as , where the sum is computed in ℤₙ. If f’ is one-to-one, then f is called a modular edge-graceful labeling and G is a modular edge-graceful graph. A modular edge-graceful labeling f of G is nowhere-zero if f(e) ≠ 0 for all e ∈ E(G) and in this case, G is a nowhere-zero modular edge-graceful graph. It is shown that a connected graph G of order n ≥ 3 is nowhere-zero...
O perfektních a kvaziperfektních grafech
O vnoření dichotomického stromu do krychle
Odd-vertex-degree trees maximizing Wiener index
On a certain ordering of the vertices of a tree
On a characterization of -trees
A graph is a -tree if either is the complete graph on vertices, or has a vertex whose neighborhood is a clique of order and the graph obtained by removing from is also a -tree. Clearly, a -tree has at least vertices, and is a 1-tree (usual tree) if and only if it is a -connected graph and has no -minor. In this paper, motivated by some properties of 2-trees, we obtain a characterization of -trees as follows: if is a graph with at least vertices, then is a -tree if...
On a matching distance between rooted phylogenetic trees
The Robinson-Foulds (RF) distance is the most popular method of evaluating the dissimilarity between phylogenetic trees. In this paper, we define and explore in detail properties of the Matching Cluster (MC) distance, which can be regarded as a refinement of the RF metric for rooted trees. Similarly to RF, MC operates on clusters of compared trees, but the distance evaluation is more complex. Using the graph theoretic approach based on a minimum-weight perfect matching in bipartite graphs, the values...
On a problem of linear arboricity
On a Spanning k-Tree in which Specified Vertices Have Degree Less Than k
A k-tree is a tree with maximum degree at most k. In this paper, we give a degree sum condition for a graph to have a spanning k-tree in which specified vertices have degree less than k. We denote by σk(G) the minimum value of the degree sum of k independent vertices in a graph G. Let k ≥ 3 and s ≥ 0 be integers, and suppose G is a connected graph and σk(G) ≥ |V (G)|+s−1. Then for any s specified vertices, G contains a spanning k-tree in which every specified vertex has degree less than k. The degree...
On acyclic colorings of direct products
A coloring of a graph G is an acyclic coloring if the union of any two color classes induces a forest. It is proved that the acyclic chromatic number of direct product of two trees T₁ and T₂ equals min{Δ(T₁) + 1, Δ(T₂) + 1}. We also prove that the acyclic chromatic number of direct product of two complete graphs Kₘ and Kₙ is mn-m-2, where m ≥ n ≥ 4. Several bounds for the acyclic chromatic number of direct products are given and in connection to this some questions are raised.
On binary representations of integers with digits .
On binary trees and permutations
Every binary tree is associated to a permutation with repetitions, which determines it uniquely. Two operations are introduced and used for the construction of the set of all binary trees. The set of all permutations which correspond to a given binary tree is determined and its cardinal number is evaluated.
On Catalan trees and the Jacobian conjecture.
On Cayley's enumeration of alkanes (or 4-valent trees).