@article{MS2_1981__48_166749,
     author = {J.M. Borwein},
     title = {A {Lagrange} multiplier theorem and a sandwich theorem for convex relations.},
     journal = {Mathematica Scandinavica},
     pages = {189--204},
     publisher = {mathdoc},
     volume = {48},
     year = {1981},
     zbl = {0468.49007},
     url = {http://geodesic.mathdoc.fr/item/MS2_1981__48_166749/}
}