Codiameters of 3-domination critical graphs with toughness more than one

A graph GG is 3-domination-critical (3-critical, for short), if its domination number γγ is 3 and the addition of any edge decreases γγ by 1. In this paper, we show that every 3-critical graph with independence number 4 and minimum degree 3 is Hamilton-connected. Combining the result with those in [Y.J. Chen, F. Tian, B. Wei, Hamilton-connectivity of 3-domination critical graphs with α≤δα≤δ, Discrete Mathematics 271 (2003) 1–12; Y.J. Chen, F. Tian, Y.Q. Zhang, Hamilton-connectivity of 3-domination critical graphs with α=δ+2α=δ+2, European Journal of Combinatorics 23 (2002) 777–784; Y.J. Chen, T.C.E. Cheng, C.T. Ng, Hamilton-connectivity of 3-domination critical graphs with α=δ+1≥5α=δ+1≥5, Discrete Mathematics 308 (2008) (in press)], we solve the following conjecture: a connected 3-critical graph GG is Hamilton-connected if and only if τ(G)>1τ(G)>1, where τ(G)τ(G) is the toughness of GG.