BORWEIN, J. M. A Lagrange multiplier theorem and a sandwich theorem for convex relations. Mathematica Scandinavica, Berkeley, CA, United States, v. 48, p. 189–204, 1981. DOI: 10.7146/math.scand.a-11911. Disponível em: https://journals.msp.org/mscand/article/view/1718. Acesso em: 25 jul. 2026.