John M. Hitchcock Aduri Pavan N. V. Vinodchandran Partial Bi-immunity, Scaled Dimension, and NP-Completeness. 131-142 2008 42 Theory Comput. Syst. 2 http://dx.doi.org/10.1007/s00224-007-9000-2 db/journals/mst/mst42.html#HitchcockPV08