1. S. K. Bose and D. Sharma,Intergral functions of two complex variables, Compositio Mathematica15 (1963), 210–226.
2. A. A. Goldberg,Elementary remarks on the formulas defining order and type of functions of several variables (Russian), Doklady Akademii Nauk Armyanskii SSR29 (1959), 145–151.
3. O. P. Juneja, G. P. Kapoor and S. K. Bajpai,On the (p, q)-order and lower (p, q)-order of an entire function, Journal für die Reine und Angewandte Mathematik282 (1976), 53–67.
4. O. P. Juneja, G. P. Kapoor and S. K. Bajpai,On the (p, q)-type and lower (p, q)-type of an entire function, Journal für die Reine und Angewandte Mathematik290 (1977), 180–190.
5. H. S. Kasana,The existence theorem for proximate order of analytic functions, Ukrainskii Matematichnii Zhurnal (Kiev)40 (1988), no. 1, 117–121, 135; English translation as Ukrainian Mathematical Journal (New York), 100–103.