1. On set-theoretical operations which preserve measurability;Lyapunov, A. A.;Doklady Akad. Nauk SSSR (N.S.),1949
2. On 𝛿𝑠-operations preserving measurability and the property of Baire;Lyapunov, A. A.;Mat. Sbornik N.S.,1949
3. \bysame, 𝑅-sets, Trudy Mat. Inst. Steklov. 40 (1953), 1-68.
4. The method of transfinite indices in the theory of operations over sets;Ljapunov, A. A.;Trudy Mat. Inst. Steklov.,1973
5. N. Lusin, Sur la classification de M. Baire, C. R. Acad. Sci. Paris 164 (1917), 91-94.