On three-dimensional hypersurfaces with type number two in $\Bbb H\sp 4$ and $\Bbb S\sp 4$ treated in intrinsic way.
(English).
In:
Slovák, Jan
and
Čadek, Martin (eds.):
Proceedings of the 23rd Winter School "Geometry and Physics".
Circolo Matematico di Palermo, Palermo, 2004.
pp. [107]-126