1. Burago, Yu., Gromov, M., Perel'man, G.: A.D. Alexandrov spaces with curvature bounded below. Uspekhi Mat. Nauk 472(284), 3-51 (1992)
2. translation in Russian Math. Surveys 47(2), 1-58 (1992)
3. Perelman, G.: Alexandrov’s spaces with curvatures bounded from below II, preprint, 1991
4. Perel'man, G.Ya.: Elements of Morse theory on Aleksandrov spaces. Algebra i Analiz 5(1), 232-241 (1993)
5. translation in St. Petersburg Math. J. 5(1), 205-213 (1994)