Constellations and projective classical groups

The constellation concept is recalled (geometrical description of a ray in a vector space). The groups PO(n + 1, C) or PSp(n + 1, C) are shown to preserve 'harmonic conjugation' between two constellations. The action of the Lorentz subgroup and its rotation subgroup is described. Finally, a theorem concerning Clebsch-Gordan product of constellations is proved. (orig.)