1. H. E. Bell, Some commutativity results for rings with two variable constraints, Proc. Amer. Math. Soc., 53 (1975), 280–285.
2. I. N. Herstein, A generalization of a theorem of Jacobson, Amer. J. Math., 73 (1951), 756–762.
3. Y. Hirano, Y. Kobayashi and H. Tominaga, Some polynomial identities and commutativity of s-unital rings, Math. J. Okayama Univ., 24 (1982), 7–13.
4. T. P. Kezlan, On identities which are equivalent with commutativity, Math. Japon., 29 (1984), 135–139.
5. H. Komatsu, A commutativity theorem for rings, Math. J. Okayama Univ., 26 (1984), 109–111.