1. Bruno, A.D.: Analytical form of differential equations (I, II). Trudy Moskov. Mat. Obsc. 25, 119–262 (1971)
2. Bruno, A.D.: Analytical form of differential equations (I, II). Trudy Moskov. Mat. Obsc. 26, 199–239 (1972). ((in Russian))
3. Bruno, A.D.: Analytical form of differential equations (I, II). Trans. Moscow Math. Soc. 25, 131–288 (1971)
4. Bruno, A.D.: Analytical form of differential equations (I, II). Trudy Moskov. Mat. Obsc. 26, 199–239 (1972). ((in English))
5. Bruno, A.D.: Local Method for Nonlinear Analysis of Differential Equations. Nauka, Moscow (1979). p. 254 ((in Russian))