1. Crabb, M.J., Duncan, J., McGregor, C.M.: Characterizations of commutativity for C*-algebras. Glasgow Math. J. 15, 172?175 (1974) MR 50:14252
2. Dixmier, J.: C*-algebras. North-Holland, New York, 1977. MR 56:16388
3. Fukamiya, M., Misonou, M., Takeda, Z.: On order and commutativity of B*-algebras. Tôhoku Math. J. (2) 6, 89?93 (1954) MR 16:376b
4. Kato, Y.: A characterization of commutative C*-algebras by normal approximate spectra. Math. Jap. 24 (1979/80), 209?210 MR 81f:46071
5. Nakanoto, R.: A spectral characterization of commutative C*-algebras. Math. Jap. 24 (1979/80), 399?400 MR 81h:46074