  Some standard definitions and results concerning foliations of dimension one
and codimension one are introduced. A proper time foliation of Minkowski space
is defined and contrasted with the foliation that is defined by the time
coordinate. The extent to which a Lorentz structure on a manifold defines
foliations, and the issues concerning the extension of the proper time
foliation of Minkowski space to a Lorentz manifold are discussed, such as
proper time sections of a geodesic flow.
