Casti, John L., Depauli, Werner (2001). Gödel: a life of logic. Basic Books, Cambridge, Mass.. DOI:10.1287/moor.1050.0169, pp. 147. ISBN 0-7382-0518-4.. From p. 80, which quotes Rudolf Gödel, Kurt's brother and a medical doctor. The words "a severe nervous crisis", and the judgement that the Schlick assassination was its trigger, are from the Rudolf Gödel quote. Rudolf knew Kurt well in those years.
