Chan, L. Y. (1978). Some approximation theorems for asymptotic functions [master's thesis, The University of Hong Kong]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0029-1812201200005265
STANKOVlC, B. (1988). S-ASYMPTOTIC EXPANSION OF DISTRIBUTIONS. International Journal of Mathematics and Mathematical Sciences, 1988(), 449-456. https://doi.org/10.1155/S0161171288000523