@article{MS2_1987__60_167020,
     author = {Christer O. Kiselman},
     title = {Smoothness of vector sums of plane convex sets.},
     journal = {Mathematica Scandinavica},
     pages = {239--252},
     publisher = {mathdoc},
     volume = {60},
     year = {1987},
     zbl = {0617.52004},
     url = {http://geodesic.mathdoc.fr/item/MS2_1987__60_167020/}
}