If a projective structure exists at any event of spacetime, the microsymmetry group that preserves that structure is a 20-parameter Lie group.

Employing the concept of the microsymmetry group (definition 4.1), Coleman and Korté (1982) have analyzed Weyl’s plasticine example in the following way: Consider a space-time manifold equipped only with a differentiable structure, the plasticine of Weyl’s example. Then our spacetime does not have an affine, conformal, projective or metric structure defined on it. In such a world it is possible do define curves and paths; however, there are no preferred curves or paths. Since there is only