1. Carleman, T.: Sur un théorème de Weierstrass. Ark. Mat. Astr. Fys. 20 B, 1–5 (1927).
2. Cooke, R.C.: Infinite matrices and sequence spaces. MacMillan & Co., London: 1950 (pp. 31–35).
3. Efimova, N.S.: Various definitions of double asymptotic expansions, and their equivalence. The problem of obtaining double asymptotic expansions by the substitution method. (Russian.) Applied questions in mathematical analysis (Russian), pp. 24–45. Tul’sk Gos. Ped. Inst., Tula, 1972. Math. Rev. 52#8751.
4. Efimova, N.S.: The problem of obtaining double asymptotic expansions by means of operational calculus. (Russian.) Applied questions in mathematical analysis (Russian), pp. 46–60. Tul’sk Gos. Ped. Inst., Tula, 1972. Math. Rev. 52#8752.
5. Eidelheit, M.: Zur Theorie der Systeme linearer Gleichungen. I, II Studia Math. 6, 139–148 (1936);