@techreport{SagnolBlancoSauvage2018, author = {Guillaume Sagnol and Marco Blanco and Thibaut Sauvage}, title = {Approximation Hierarchies for the cone of flow matrices}, institution = {ZIB}, address = {Takustr. 7, 14195 Berlin}, number = {18-20}, language = {eng}, year = {2018} }