  The notion of incompressible momentum observables is introduced. It is shown
that when the metric in a manifold has a certain form, a set of canonically
conjugate variables Xk and Pk in which Pk are incompressible, can be
constructed. Based on this set of variables, the quantum mechanical description
of the motion of a particle in a manifold, is identical to that associated with
the familiar canonically conjugate variables xk and pk in an Euclidean space
with Cartesian coordinates. The controversy related to non-uniqueness of
momentum operators when the range of a coordinate is a finite interval is
reduced to two possible extensions. This suggests relating these two types of
extensions to the type of particle as being fermion or boson.
