1. C. Badea and C. Cottin, Korovkin-type Theorems for Generalized Boolean Sum Operators, Colloquia Mathematica Societatis János Bolyai, 58, Approximation Theory, Kecskemét (Hungary), 1990, pp. 51-67.
2. D. Bărbosu, Polynomial Approximation by Means of Schurer-Stancu type Operators, Editura Universităţii de Nord Baia Mare, 2006.
3. G.H. Kirov, A generalization of the Bernstein polynomials, Math. Balkanica, New Series, 6 (1992) no. 2, pp. 147-153.
4. O.T. Pop, The generalization of Voronovskaja's theorem for a class of linear and positive operators, Rev. Anal. Numér. Théor. Approx., 34 (2005) no. 1, pp. 79-91, http://ictp.acad.ro/jnaat/journal/article/view/2005-vol34-no1-art9
5. O.T. Pop, About some linear and positive operators defined by infinite sum, Dem. Math., XXXIX (2006) no. 2, pp. 377-388, https://doi.org/10.1515/dema-2006-0216