1. J. A. Minahan, P. Ramond, and R. C. Warner, “Comment on anomaly cancellation in the standard model,” Phys. Rev. D, 41, 715–716 (1990).
2. A. Bilal, “Lectures on anomalies,” arXiv: 0802.0634.
3. H. Georgi and S. L. Glashow, “Unity of all elementary-particle forces,” Phys. Rev. Lett., 32, 438–441 (1974).
4. R. N. Mohapatra, Unification and Supersymmetry. The Frontiers of Quark-Lepton Physics: The Frontiers of Quark-Lepton Physics, Springer, New York (2002).
5. J. R. Ellis, S. Kelley, and D. V. Nanopoulos, “Probing the desert using gauge coupling unification,” Phys. Lett. B, 260, 131–137 (1991).