\Bibitem{Sin66}
\by G.~Kh.~Sindalovskii
\paper On the total differential
\jour Sb. Math.
\yr 1966
\vol 112
\issue 3
\mathnet{http://mi.mathnet.ru/eng/sm4229}
\mathscinet{https://mathscinet.ams.org/mathscinet-getitem?mr=199321}
\zmath{https://zbmath.org/?q=an:0163.06501}