Chromatic Uniqueness of Certain Bipartite Graphs with Six Edges Deleted

For integers p, q, s with p >= q >= 2 and s >= 0, let K-2(-s) (p, q) denote the set of 2-connected bipartite graphs which can be obtained from K-p,K-q by deleting a set of s edges. F.M.Dong et al. (Discrete Math. vol.224 (2000) 107-124) proved that for any graph G is an element of K-2(-s) (p, q) with p >= q >= 3 and 0 <= s <= min {4, q - 1}, then G is chromatically unique. In this paper, we study the chromaticity of any graph G is an element of K-2(-s) (p, q) when p >= 6, q = 4 and s = 6.