1. Popper, Karl , n.d. Single page fragment concerning Bühler. [typescript.] Popper Collection, Hoover Institute Archives, Stanford University (3:37).
2. Milford (Hilferding), P. , 1999. Interview with Malachi Haim Hacohen at home of Karl Milford (Vienna) (recording tape & typescript.) 30 January.
3. Kraft, J. (anon.), 1932. Letter to Karl Popper, 29 July. Popper Collection, Hoover Institute Archives, Stanford University (210: 3).
4. ‘Die östereichischen Grenzlogen’;Hubert;Quatuor- Coronati-Jahrbuch,1983