\Bibitem{Vas55}
\by M.~V.~Vasil'eva
\paper Geometry of an integral
\jour Sb. Math.
\yr 1955
\vol 78
\issue 1
\mathnet{http://mi.mathnet.ru//eng/sm5180}
\mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=67558}
\zmath{https://zbmath.org/?q=an:0064.40901}