Chandok, S., & Narang, T. D. (2011). Invariant Points and ε-Simultaneous Approximation. International Journal of Mathematics and Mathematical Sciences, 2011(), 992-1001-082. https://doi.org/10.1155/2011/579819
Liu, M. C. (1969). Some applications of asymptotic approximation [master's thesis, The University of Hong Kong]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0029-1812201200009898