In the branch of mathematical logic known as type theory, System F<:, pronounced "F-sub", is an extension of system F with subtyping. System F<: has been of central importance to programming language theory since the 1980s because the core of functional programming languages, like those in the ML family, support both parametric polymorphism and record subtyping, which can be expressed in System F<:.
- 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.
- Pierce, Benjamin (2002). Types and Programming Languages. MIT Press. ISBN 978-0-262-16209-8., Chapter 26: Bounded quantification