From that entry... The indefinability theorem is conventionally attributed to Alfred Tarski. Gödel also discovered the indefinability theorem in 1930, while pr

From that entry... The indefinability theorem is conventionally attributed to Alfred Tarski. Gödel also discovered the indefinability theorem in 1930, while proving his incompleteness theorems published in 1931, and well before the 1936 publication of Tarski's work (Murawski 1998). While Gödel never published anything bearing on his independent discovery of indefinability, he did describe it in a 1931 letter to John von Neumann.