JOUAK, Mohamed; THIBAULT, Lionel. Directional derivates and almost everywhere differentiability of biconvex and concave-convex operators. Mathematica Scandinavica, Berkeley, CA, United States, v. 57, p. 215–224, 1985. DOI: 10.7146/math.scand.a-12113. Disponível em: https://journals.msp.org/mscand/article/view/1555. Acesso em: 25 jul. 2026.