@article {aksen2013bilevel, title = {A bilevel p-median model for the planning and protection of critical facilities}, journal = {Journal of Heuristics}, volume = {19}, number = {2}, year = {2013}, pages = {373{\textendash}398}, publisher = {Springer US}, author = {Aksen, Deniz and Necati Aras and Piyade, Nuray} }