\Bibitem{Kov60}
\by N.~I.~Kovantsov
\paper Canonical quadrics of a complex of lines in projective space
\jour Sb. Math.
\yr 1960
\vol 92
\issue 2
\mathnet{http://mi.mathnet.ru/eng/sm4785}
\mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=117673}
\zmath{https://zbmath.org/?q=an:0114.37303}