On Zurek's derivation of the born rule

Recently, W. H. Zurek presented a novel derivation of the Born rule based on a mechanism termed environment-assisted invariance, or envariance [ W. H. Zurek, Phys. Rev. Lett. 90( 2), 120404 ( 2003)]. We review this approach and identify fundamental assumptions that have implicitly entered into it, emphasizing issues that any such derivation is likely to face.