Cường, Bùi Công, Hoàng Việt long, and Phạm Hồng Phong. 2012. “On the Approximation of Continous Function by Spline Function Hireachical Fuzzy Systems”. Journal of Computer Science and Cybernetics 25 (2):99-108. https://doi.org/10.15625/1813-9663/25/2/563.