This paper presents some new results on permissible degree sets in polygon visibility graphs (PVGs). If the PVG has \( n \) vertices, we say it is an \( n \)-PVG. We also show some canonical construction techniques for PVGs with given degree sets.

In this paper, we present several graph theory related software systems that we have developed. These systems have been used in learning and research. The systems feature drawing and manipulation of graphs as well as execution of graph algorithms. The systems are: JGraph, a Java-based system for creating graphs and running graph algorithms; Colossus, a visibility graph system; Manohar, a system for computing graceful labelings of graphs (with special emphasis on trees); Graph Algorithm Constructor, which allows the creation of graph algorithms by drawing flow diagrams instead of writing source code. We also describe some examples in which the empirical data generated from these systems have allowed us to discover fundamental properties of graphs.

A simple acyclic graphoidal cover of a graph \( G \) is a collection \( \psi \) of paths in \( G \) such that every path in \( \psi \) has at least two vertices, every vertex of \( G \) is an internal vertex of at most one path in \( \psi \), every edge of \( G \) is in exactly one path in \( \psi \), and any two paths in \( \psi \) have at most one vertex in common. The minimum cardinality of a simple acyclic graphoidal cover of \( G \) is called the simple acyclic graphoidal covering number of \( G \) and is denoted by \( \eta_{as}(G) \). A simple acyclic graphoidal cover \( \psi \) of \( G \) with \( |\psi| = \eta_{as}(G) \) is called a minimum simple acyclic graphoidal cover of \( G \). Two minimum simple acyclic graphoidal covers \( \psi_1 \) and \( \psi_2 \) of \( G \) are said to be isomorphic if there exists an automorphism \( \alpha \) of \( G \) such that \( \psi = \{\alpha(P) : P \in \psi_1\} \). In this paper, we characterize trees, unicyclic graphs, and wheels in which any two minimum simple acyclic graphoidal covers are isomorphic.

In this paper, we study the domination number, the global domination number, the cographic domination number, the global cographic domination number, and the independent domination number of all the graph products which are non-complete extended \( p \)-sums (NEPS) of two graphs.

A sum composite labeling of a \((p,q)\) graph \( G = (V,E) \) is an injective function \( f : V(G) \to \{1,2,\dots,2p\} \) such that the function \( f^+ : E(G) \to C \) is also injective, where \( C \) denotes the set of all composite numbers and \( f^+ \) is defined by \( f^+(uv) = f(u) + f(v) \) for all \( uv \in E(G) \). A graph \( G \) is sum composite if there exists a sum composite labeling for \( G \). We give some classes of sum composite graphs and some classes of graphs which are not sum composite. We prove that it is possible to embed any graph \( G \) with a given property \( P \) in a sum composite graph which preserves the property \( P \), where \( P \) is the property of being connected, eulerian, hamiltonian, or planar. We also discuss the NP-completeness of the problem of determining the chromatic number and the clique number of sum composite graphs.

A \((p,q)\)-graph \( G \) is said to be \((k,d)\)-multiplicatively indexable if there exists an injection \( f : V(G) \to \mathbb{N} \) such that \( f^\times(E(G)) = \{k,k+d,\dots,k+(q-1)d\} \), where \( f^\times : E(G) \to \mathbb{N} \) is defined by \( f^\times(uv) = f(u)f(v) \) for every \( uv \in E(G) \). If further \( f(V(G)) = \{1,2,\dots,p\} \), then \( G \) is said to be a \((k,d)\)-strongly multiplicatively indexable graph. In this paper, we initiate a study of graphs that admit such labellings.

Public Key Cryptosystems (PKC) based on formal language theory and semi groups have been of interest and study. A PKC based on free group has been presented in [7]. Subsequently, another PKC using free partially commutative monoids and groups is studied in [1]. In this paper, we propose a PKC for chain cade pictures that uses a finitely presented group for encryption and free group for decryption. Also, we present another PKC for line pictures in the hexagonal grid, which uses a finitely presented group for encryption and finitely presented free partially commutative group for decryption.

Let \( G = (V, E) \) be a connected graph. A subset \( A \) of \( V \) is called an asteroidal set if for any three vertices \( u,v,w \) in \( A \), there exists a \( u \)-\( v \) path in \( G \) that avoids the neighbourhood of \( w \). The asteroidal chromatic number \( \chi_a \) of \( G \) is the minimum order of a partition of \( V \) into asteroidal sets. In this paper we initiate a study of this parameter. We determine the value of \( \chi_a \) for several classes of graphs, obtain sharp bounds, and Nordhaus-Gaddum type results.