Conversation so far:
In what year was On Formally Undecidable Propositions of Principia Mathematica and Related Systems I published?
On Formally Undecidable Propositions of Principia Mathematica and Related Systems I by Kurt Gödel was dated November 17, 1930, and originally published in 1931 volume of Monatshefte für Mathematik.
At what age did Kurt Godel join his brother in Vienna?
At the age of 18, Kurt Gödel joined his brother in Vienna and entered the University of Vienna.

Question: In what year did he complete his doctoral?
Self-contained rewrite: In what year did Kurt Gödel complete his doctoral?