  In this paper, we present a general theory of motion planning for kinematic
systems. This theory has been developed for long by one of the authors in a
previous series of papers. It is mostly based upon concepts from subriemannian
geometry. Here, we summarize the results of the theory, and we improve on, by
developping in details an intricated case: the ball with a trailer, which
corresponds to a distribution with flag of type 2,3,5,6.
  This paper is dedicated to Bernard Bonnard for his 60th birthday.
