Absolute continuity on tracks and mappings of Sobolev spaces

Calkin, J. W., Functions of several variables and absolute continuity I. Duke Math. J. 6, 170–186 (1940).

Federer, H., Geometric Measure Theory (Grundlehren d. Math. Wiss., Vol. 153). New York: Springer (1969).

Gagliardo, E., Proprietà di alcune classi di funzioni in più variabili. Richerche di Mat. 7, 102–137 (1958).

Morrey, C. B., Functions of several variables and absolute continuity II. Duke Math. J. 6, 187–215 (1940).

Roger, F., Sur la relation entre les propriétés tangentielles et metriques des ensembles cartésiens. C. R. Acad. Sci. Paris 201, 871–872 (1935).

Saks, S., Theory of the Integral. Second ed. (Monografje Math., Vol. 7) Warsaw, 1937. Reprinted Stechert-Hafner Pub. Co., New York. New York: Dover 1964.

Serrin, J., Personal communication, 1971.

Serrin, J., & D. E. Varberg, A general chain rule for derivatives and the change of variables formula for the Lebesgue integral. Amer. Math. Monthly 76, 514–520 (1969)

Sobolev, S. L., Applications of Functional Analysis in Mathematical Physics (Transl, of Math. Monographs, Vol. 7). Providence, Amer. Math. Soc., 1963.

Vallée Poussin, Ch. J. de la, Sur l'intégrale de Lebesgue. Trans. Amer. Math. Soc. 16, 435–501 (1915).