Henningsen, Arne, and Jeff D. Hamann. “Systemfit: A Package for Estimating Systems of Simultaneous Equations in R”. Journal of Statistical Software 23, no. 4 (December 31, 2007): 1–40. Accessed April 18, 2024. https://www.jstatsoft.org/index.php/jss/article/view/v023i04.