In this paper we study the L(2, 1)-labeling problem on oriented planar graphs with particular attention on the subclasses of oriented prisms, Halin and cactus graphs. For these subclasses more accurate results are presented. keywords: L(2, 1)-labeling, oriented graph coloring, digraphs, prisms, Halin graphs, cacti.

LetD = (V (D), A(D)) be a digraph; a kernelN ofD is a set of verticesN ⊆ V (D) such that N is independent (for any x, y∈N there is no arc between them) and N is absorbent (for each x ∈ V (D) −N) there exists an xN -arc in D). A digraph D is said to be kernel-perfect whenever each one of its induced subdigraphs has a kernel. A digraph D is oriented by sinks when every semicomplete subdigraph of ...

2007 is a jubilee year: in 1967, programming language SIMULA 67 was presented, which contained all aspects of what was later called object-oriented programming. The present paper contains a description of the development unto the objectoriented programming, the role of simulation in this development and other tools that appeared in SIMULA 67 and that are nowadays called super-object-oriented pr...

A perfect sequence has the optimal periodic autocorrelation function where all out-of-phase values are zero, and an orthogonal set has orthogonality that the periodic correlation function for any pair of distinct sequences in the set takes zero at the zero shift. The real-valued perfect sequences of period N = 2 are derived from a real-valued Huffman sequence of length 2 + 1 with ν ≥ n whose ou...

Let γ(G) and ι(G) be the domination and independent domination numbers of a graph G, respectively. Introduced by Sumner and Moorer [23], a graph G is domination perfect if γ(H) = ι(H) for every induced subgraph H ⊆ G. In 1991, Zverovich and Zverovich [26] proposed a characterization of domination perfect graphs in terms of forbidden induced subgraphs. Fulman [15] noticed that this characterizat...