There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

A graph is just a bunch of points with lines between some of them, like a map of cities linked by roads. A rather simple notion. Nevertheless, the theory of graphs has broad and important applications, because so many things can be modeled by graphs. For example, planar graphs — graphs in which none of the lines cross are— important in designing computer chips and other electronic circuits. Also, various puzzles and games are solved easily if a little graph theory is applied.

A Theory of Graphs

A survey of selected recent results on total domination in graphs

A survey of Nordhaus-Gaddum type relations

Note: On the Roman domination number of a graph

On the double Roman domination in graphs

Varieties of Roman domination II

For a positive integer k, a k-rainbow dominating function of a graph G is a function f from the vertex set V (G) to the set of all subsets of the set {1, 2, . . . , k} such that for any vertex v ∈ V (G) with f(v) = ∅ the condition ⋃ u∈N(v) f(u) = {1, 2, . . . , k} is fulfilled, where N(v) is the neighborhood of v. The 1-rainbow domination is the same as the ordinary domination. A set {f1, f2, . . . , fd} of k-rainbow dominating functions on G with the property that ∑ d i=1 |fi(v)| ≤ k for each v ∈ V (G), is called a k-rainbow dominating family (of functions) on G. The maximum number of functions in a krainbow dominating family on G is the k-rainbow domatic number of G, denoted by drk(G). Note that dr1(G) is the classical domatic number d(G). In this paper we initiate the study of the k-rainbow domatic number in graphs and we present some bounds for drk(G). Many of the known bounds of d(G) are immediate consequences of our results.

Seyed Mahmoud Sheikholeslami

Papers

Note: On the Roman domination number of a graph

On the double Roman domination in graphs

Varieties of Roman domination II

The k-rainbow domatic number of a graph

Nordhaus―Gaddum bounds on the k-rainbow domatic number of a graph