1.
Test.
2.
The Collected Papers of Albert Einstein, Volume 14: The Berlin Years: Writings & Correspondence, April 1923-May 1925. (Princeton University Press; Documentary edition, 13AD).
3.
The Collected Papers of Albert Einstein, Volume 13. (English): The Berlin Years: Writings & Correspondence, January 1922 - March 1923. (Princeton University Press; Documentary edition, 21AD).