Rivero, A. C., Korobov, V., & Skoryk, V. (2004). The controllability function as the time of motion. IIThe controllability function as the time of motion. II. Mathematical Physics, Analysis, Geometry, 11(3), 341–354. Retrieved from http://mag.ilt.kharkiv.ua/index.php/mag/article/view/m11-0341r