Rules for Integrals over Products of Distributions from Coordinate   Independence of Path Integrals
  In perturbative calculations of quantum mechanical path integrals in curvilinear coordinates, Feynman diagrams involve multiple temporal integrals over products of distributions, which are mathematically undefined. We derive simple rules for their evaluation from the requirement of coordinate independence of path integrals. 
H. Kleinert, A. Chervyakov