Problem 2. Please read from Callen, how the polymer model is done
"in two dimensions"
(pages 339-43, here is a "shortcut":
please click! Then, consider a
simpler, one-dimensional model, and solve problem 3.34 from D.V.
Schroeder's book (p. 114). (you may also look at Slide #18
in this PPT presentation available on the Web, it gives some hints).