A Remark on Non-equivalent Star Products via Reduction for CP^n
  In this paper we construct non-equivalent star products on CP^n by phase space reduction. It turns out that the non-equivalent star products occur very natural in the context of phase space reduction by deforming the momentum map of the U(1)-action on C^{n+1} {0} into a quantum momentum map and the corresponding momentum value into a quantum momentum value such that the level set, i.~e. the `constraint surface', of the quantum momentum map coincides with the classical one. All equivalence classes of star products on CP^n are obtained by this construction. 
Stefan Waldmann