  In 2011 I reviewed the calculation by Onsager and Kaufman of the spontaneous
magnetization of the square-lattice Ising model, which Onsager announced in
1949 but never published. I have recently been alerted to further original
papers that bear on the subject. It is quite clear that the draft paper on
which I relied was indeed written by Onsager, who was working on the problem
with Kaufman, and that they had two derivations of the result.
