1. Hufschmidt, T., A type-system for Nix. http://nixcon2017.org/schedule.nixcon2017.org/system/event_attachments/attachments/000/000/003/original/main.pdf.
2. Siek, J. and Taha, W., Gradual typing for objects, Proc. European Conf. on Object-Oriented Programming (ECOOP), Ernst, E., Ed., Berlin: Springer, 2007, pp. 2–27.
3. Levkivskyi, I., Lehtosalo, J., and Langa, L., PEP 544 – Protocols: Structural subtyping (static duck typing). http://www.python.org/dev/peps/pep-0544. Accessed January 10, 2019.
4. Turchin, V.F., Meta-algorithmic language, Kibernetika, 1968, no. 4, pp. 45–54.
5. Turchin, V.F., REFAL-5: Programming Guide and Reference Manual, Holyoke: New England, 1989.