I found the following quote in this paper:
Wilson, Kenneth G. "The renormalization group and critical phenomena." Reviews of Modern Physics 55.3 (1983): 583.
Later, Jon Mathews explained some of Feynman's tricks for reproducing the solution for the two-dimensional Ising model. I didn't follow what Jon was saying ...
Is there somewhere one can read about what Feynman tricks this quote is referring to?