Classical BRST charge and observables in reducible gauge theories
  We study the construction of the classical Becchi-Rouet-Stora-Tyutin (BRST) charge and observables for arbitrary reducible gauge theory. Using a special coordinate system in the extended phase space, we obtain an explicit expression for the Koszul-Tate differential operator and show that the BRST charge can be found by a simple iterative method. We also give a formula for the classical BRST observables. 
Andrei V. Bratchikov
hep-th math-ph math.MP