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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.

Question: At what age did Godel join his brother in Vienna?
Self-contained rewrite: At what age did Kurt Godel join his brother in Vienna?