Comment on "Kirchhoff index in line, subdivision and total graphs of a regular graph"

Let G be a connected regular graph. Denoted by t(G) and Kf (G) the total graph and Kirchhoff index of G, respectively. This paper is to point out that Theorem 3.7 and Corollary 3.8 from "Kirchhoff index in line, subdivision and total graphs of a regular graph" [X. Gao, Y.F. Luo, W.W. Liu, Kirchhoff index in line, subdivision and total graphs of a regular graph, Discrete Appl. Math. 160(2012) 560-565] are incorrect, since the conclusion of a lemma is essentially wrong. Moreover, we first show the Laplacian characteristic polynomial of t(G), where G is a regular graph. Consequently, by using Kf(G), we give an expression on Kf (t(G)) and a lower bound on Kf (t(G)) of a regular graph G, which correct Theorem 3.7 and Corollary 3.8 in Gao et al. (2012) [2]. (C) 2013 Elsevier B.V. All rights reserved.