Anna Bernasconi Valentina Ciriani Roberto Cordone The optimization of kEP-SOPs: Computational complexity, approximability and experiments. 2008 13 ACM Trans. Design Autom. Electr. Syst. 2 http://doi.acm.org/10.1145/1344418.1344431 db/journals/todaes/todaes13.html#BernasconiCC08