Mohapatra, R. N., and B. N. Sahney. “Approximation of Continuous Functions by Their Fourier Series”. Anal. Numér. Théor. Approx., vol. 10, no. 1, Feb. 1981, pp. 81-87, https://ictp.acad.ro/jnaat/journal/article/view/1981-vol10-no1-art9.