Mixed virtual element methods for general second order elliptic problems on polygonal meshes Lourenço Beirão da Veiga, Franco Brezzi, Luisa Donatella Marini and Alessandro Russo ESAIM: M2AN, 50 3 (2016) 727-747 Published online: 23 May 2016 DOI: 10.1051/m2an/2015067