  Galilei’s inertial law shows, that there exists a type of  constraining guidance in the world [spacetime] that imposes on a body that is let free in some definite world direction a unique  natural motion from which it can only be diverted through external  forces; this occurs on the basis of an effective infinitesimal  tendency of persistence from point to point, that  auto-parallelly transfers the world direction \(r\) of  the body at an arbitrary point \(P\) to an infinitesimally close  neighboring point \(P'\), that lies in the direction  \(r\) at \(P\).