I want to know the answer to the following question:
What 2 techniques did Von Neumann use to exclude sets in his doctoral thesis in 1925?
All the background I'm provided with is that "At the beginning of the 20th century, efforts to base mathematics on naive set theory suffered a setback due to Russell's paradox (on the set of all sets that do not belong to themselves).". Is that enough to answer the question?
Answer: no