Ramkumar Chinchani Duc T. Ha Anusha Iyer Hung Q. Ngo Shambhu J. Upadhyaya On the Hardness of Approximating the Min-Hack Problem. 295-311 2005 9 J. Comb. Optim. 3 http://dx.doi.org/10.1007/s10878-005-1413-8 db/journals/jco/jco9.html#ChinchaniHINU05