Letters written by Gregory Bateson to Norbert Wiener in the 1950s, articulating his theory of double binds. The letters (especially #3) also say something about the analytic productivity of collaboration.
Bateson, Gregory. 2017. “‘Minimum Constellation Necessary for Type Confusion’: Letters to Norbert Wiener.” Grey Room, no. 66 (January): 115–19. https://doi.org/10.1162/GREY_a_00214.