Moshe Dror Gerd Finke Sylvain Gravier Wieslaw Kubiak On the complexity of a restricted list-coloring problem. 103-109 1999 195 Discrete Mathematics 1-3 http://dx.doi.org/10.1016/S0012-365X(98)00169-1 db/journals/dm/dm195.html#DrorFGK99