HOFFMANN-JORGENSEN, J. On the Differentiability Points of a Function of Two Real Variables Admitting Partial Derivatives. Mathematica Scandinavica, Berkeley, CA, United States, v. 35, p. 259–266, 1974. DOI: 10.7146/math.scand.a-11551. Disponível em: https://journals.msp.org/mscand/article/view/2098. Acesso em: 25 jul. 2026.