Tsang, K. M. (1980). Some theorems in diophantine approximation [master's thesis, The University of Hong Kong]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0029-1812201200005259
Velrajan, M., & Asokkumar, A. (2010). Note on Isomorphism Theorems of Hyperrings. International Journal of Mathematics and Mathematical Sciences, 2010(), 430-441. https://doi.org/10.1155/2010/376985