BORWEIN, J. M. A Lagrange multiplier theorem and a sandwich theorem for convex relations. MATHEMATICA SCANDINAVICA, [S. l.], v. 48, p. 189–204, 1981. DOI: 10.7146/math.scand.a-11911. Disponível em: https://tidsskrift.dk/math/article/view/11911. Acesso em: 14 aug. 2026.