Reductions of path structures and classification of homogeneous structures in dimension three

Abstract: In this paper we show that if a path structure has non-vanishing curvature at apoint then it has a canonical reduction to a Z/2Z-structure at a neighbourhood of thatpoint (in many cases it has a canonical parallelism). A simple implication of this resultis that the automorphism group of a non-flat path structure is of maximal dimensionthree (a result by Tresse of 1896). We also classify the invariant path structures onthree-dimensional Lie groups.