Groups, Algorithms, and Programming (GAP) are a system for computational discrete algebra, with particular emphasis on Computational Group Theory. GAP provides a programming language, a library of thousands of functions implementing algebraic algorithms written in the GAP language as well as large data libraries of algebraic objects. The first version of GAP was operational by the end of 1986. The system was first presented at the Oberwolfach meeting on computational group theory in May 1988. Officially, Version 2.4 was the first to be given away from Aachen starting in December 1988. A topological index of a molecular graph is a real number derived from the structure of the graph such that isomorphic graphs have the same topological index. The chemical graph theory is a branch of mathematical chemistry that is mostly concerned with finding topological indices of chemical graphs that correlate well with certain physicochemical properties of the corresponding molecules.