Girard, Jean-Yves (1986). "The system F of variable types, fifteen years later". Theoretical Computer Science. 45: 160. doi:10.1016/0304-3975(86)90044-7. However, in [3] it was shown that the obvious rules of conversion for this system, called F by chance, were converging.
Cardelli, Luca; Martini, Simone; Mitchell, John C.; Scedrov, Andre (1994). "An extension of system F with subtyping". Information and Computation, vol. 9. North Holland, Amsterdam. pp. 4–56. doi:10.1006/inco.1994.1013.