Cường, B.C., long, H.V. and Phong, P.H. 2012. On the approximation of continous function by spline function hireachical fuzzy systems. Journal of Computer Science and Cybernetics. 25, 2 (Apr. 2012), 99–108. DOI:https://doi.org/10.15625/1813-9663/25/2/563.