Fève, F., Florens, J.-P., & Van Keilegom, I. (2018). Estimation of Conditional Ranks and Tests of Exogeneity in Nonparametric Nonseparable Models. Journal of Business and Economic Statistics, 36(2), 334-345. https://doi.org/10.1080/07350015.2016.1166120 (Original work published 2018)