two parametric space motions; Darboux-theorem; kinematics geometry
The paper contains the proof of the classification theorem for two-parametric space motions with at least 5 points with plane trajectories. The proof is based on  and on the cannonical form of a certain tensor of order 3. The second part of the paper deals with the problem of plane trajectories from the differential-geometrical point of view. Some applications are given.
 G. Koenigs: Leçons de Cinématique. Paris 1897, Note III by G. Darboux: Sur les mouvements algébriques.
 A. Karger: Two-parametric motions in $E_3$
. Apl. mat. 32 (1987), 96-119. MR 0885757