@article{EP_1998_4_a17,
     author = {E. Casas and F. Tr\"oltzsch and A. Unger},
     title = {Second order sufficient optimality conditions for a class of elliptic control problems},
     journal = {ESAIM. Proceedings},
     pages = {285--300},
     publisher = {mathdoc},
     volume = {4},
     year = {1998},
     doi = {10.1051/proc:1998034},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1051/proc:1998034/}
}