  During his last year of life Feynman became interested in integrable models.
In the course of his study of one dimensional particles with inverse
square-type potentials (the Calogero class of models) he came up with a field
theory-inspired proof of the commutativity of the integrals of motion of the
system, which remained unpublished. I present an exact transcript of the proof
together with a scan of the first page of Feynman's original manuscript and
some historical background.
