Stanilov, Grozó:
Геодезическая нормаль к поверхности в $P_3$.
(Russian) [The geodesic normal to a surface in $P_3$].Commentationes Mathematicae Universitatis Carolinae,
vol. 5
(1964),
issue 1,
pp. 33-36
Stanilov, Grozó:
К биaкcиaльнoй тeopии кoнгpуэнции пpямыx.
(Russian) [On the bi-axial theory of a congruence of lines].Commentationes Mathematicae Universitatis Carolinae,
vol. 4
(1963),
issue 3,
pp. 117-120