Jaan Raik Raimund Ubar Anna Krivenko Margus Kruus Hierarchical Identification of Untestable Faults in Sequential Circuits. 668-671 2007 DSD http://dx.doi.org/10.1109/DSD.2007.4341539 conf/dsd/2007 db/conf/dsd/dsd2007.html#RaikUKK07