Nesrine Abbas Joseph C. Culberson Lorna Stewart Recognizing Maximal Unfrozen Graphs with respect to Independent Sets is CO-NP-complete. 141-154 2005 7 Discrete Mathematics & Theoretical Computer Science 1 http://www.dmtcs.org/volumes/abstracts/dm070110.abs.html db/journals/dmtcs/dmtcs7.html#AbbasCS05