Avdzhieva, A., V. Gushev, and G. Nikolov. “DEFINITE QUADRATURE FORMULAE OF ORDER THREE WITH EQUIDISTANT NODES”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 104, Dec. 2017, pp. 155-70, https://annual.uni-sofia.bg/index.php/fmi/article/view/42.