A. Blokhuis et P. Sziklai, A NOTE ON SMALL COMPLETE CAPS IN THE KLEIN QUADRIC, Bulletin of the Belgian Mathematical Society Simon Stevin, 5(2-3), 1998, pp. 159-161
We give a lower bound for the size of a cap being contained and comple
te in the Klein quadric in PG(5, q), or equivalently, for the size of
a set C of lines in PG(3, q) such that no three of them are concurrent
and coplanar in the same time, and being also maximal for this proper
ty.