@article{Borwein_1981, title={A Lagrange multiplier theorem and a sandwich theorem for convex relations.}, volume={48}, url={https://www.mscand.dk/article/view/11911}, DOI={10.7146/math.scand.a-11911}, journal={MATHEMATICA SCANDINAVICA}, author={Borwein, J. M.}, year={1981}, month={Dec.}, pages={189–204} }