For the projective unitary group P U n PUₙ with a maximal torus T P U n Tₔ䂸 and Weyl group W W, we show that the integral restriction homomorphism \ ρ P U n: H ∗ (B P U n ; Z) → H ∗ (B T P U n ; Z) W ₔ䂸 H^* (BPUₙ; Z) H^* (BTₔ䂸; Z) W \ to the integral invariants of the Weyl group action is onto. We also present several rings naturally isomorphic to H ∗ (B T P U n ; Z) W H^* (BTₔ䂸; Z) W. In addition we give general sufficient conditions for the restriction homomorphism ρ G G to be onto for a connected compact Lie group G G.
Crowley et al. (Wed,) studied this question.