#Gödel #EmilPost #VonNeumann #recursivity “I do not know if you have heard that "Post's problem", whether there are degrees of unsolvability among problems of the form (∃ y) φ(y,x), where φ is recursive, has been solved in the positive sense by a very young man by the name of Richard Friedberg. The solution is very elegant. Unfortunately, Friedberg does not intend to study mathematics, but rather medicine.” Gödel to Von Neumann