References for Alexander Friedmann

    1. Biography in Dictionary of Scientific Biography (New York 1970-1990).
    2. Biography in Encyclopaedia Britannica.
    1. E A Tropp, V Ya Frenkel and A D Chernin, Alexander A. Friedmann : the man who made the universe expand (Cambridge, 1993).
    1. A F Gavrilov, In memory of A S Friedmann, Uspekhi fizicheskikh nauk 6 (1926), 73-75.