Reply to the Comment of X. Ji on "Spin and orbital angular momentum in   gauge theories" [PRL 100:232002 (2008)]
  We reply to the Comment of X. Ji [arXiv:0810.4913] on our paper [PRL 100:232002 (2008)], concerning angular momentum algebra, locality, Lorentz covariance, and measurability of our gauge-invariant description of the spin and orbital angular momentum of quarks and gluons. 
Xiang-Song Chen, Xiao-Fu L\"u, Wei-Min Sun, Fan Wang, and T. Goldman