Equivalence of star products

We give an elementary proof of the fact that equivalence classes of smooth or differentiable star products on a symplectic manifold M are parametrized by sequences of elements in the second de Rham cohomology space of the manifold. The parametrization is given explicitly in terms of Fedosov's construction which yields a star product when one chooses a symplectic connection and a sequence of closed 2-forms on M, We also show how derivations of a given star product. module inner derivations, are parametrized by sequences of elements in the first de Rham cohomology space of M.