Given a graph G, the atom-bond connectivity (ABC) index is defined to be ABC(G) = ..., where E(G) is the edge set of graph G and dG(v) is the degree of vertex v in graph G. The paper [6] claims to classify those trees with a fixed number of leaves which minimize the ABC index. Unfortunately, there is a gap in the proof leading to other examples that contradict the main result of that work. These examples and the problem are discussed in this work.
