@article{MS2_1974__34_166345,
     author = {Soren Johansen},
     title = {The {Extremal} {Convex} {Functions.}},
     journal = {Mathematica Scandinavica},
     pages = {61--68},
     publisher = {mathdoc},
     volume = {34},
     year = {1974},
     zbl = {0286.26002},
     url = {http://geodesic.mathdoc.fr/item/MS2_1974__34_166345/}
}