  A spherical system is a combinatorial object, arising in the theory of
wonderful varieties, defined in terms of a root system. All spherical systems
can be obtained by means of some general combinatorial procedures (such as
parabolic induction and wonderful fiber product) from the so-called primitive
spherical systems. Here we classify primitive spherical systems. As an
application, we prove that the quotients of a spherical system are in
correspondence with the so-called distinguished subsets of colors.
