1. P.N. Agrawal, V. Gupta, Simultaneous approximation by linear combination of modified Bernstein polynomials. Bull. Greek Math. Soc. 39, 29–43 (1989)
2. L. Bingzhang, Direct and converse results for linear combinations of Baskakov–Durrmeyer operators. Approx. Theory Appl. 9(3), 61–72 (1993)
3. Z. Ditzian, V. Totik, Moduli of Smoothness (Springer, Berlin, 1987)
4. V. Gupta, R.P. Agarwal, Convergence Estimates in Approximation Theory (Springer, Cham, 2014)
5. V. Gupta, G. Tachev, Approximation by Szász-Mirakyan Baskakov operators. J. Appl. Funct. Anal. 9(3–4), 308–319 (2014)