  The main theme of the article is the study of discrete systems of material
points subjected to constraints not only of a geometric type (holonomic
constraints) but also of a kinematic type (nonholonomic constraints). The
setting up of the equations of motion follows a simple principle which
generalizes the holonomic case. Furthermore, attention is paid to the fact that
the kinematic variables retain their velocity meaning, without resorting to the
pseudo-velocity technique. Particular situations are examined in which the
modeling of the constraints can be carried out in several ways to evaluate
their effective equivalence. Numerous examples, many of which taken from the
most recurring ones in the literature, are provided in order to illustrate the
proposed theory.
