\Bibitem{Rod55}
\by A.~M.~Rodnyanskii
\paper Differentiable mappings and the order of connectivity
\jour Sb. Math.
\yr 1955
\vol 79
\issue 1
\mathnet{http://mi.mathnet.ru/eng/sm5208}
\mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=72462}
\zmath{https://zbmath.org/?q=an:0066.41303}