Negative results in coconvex approximation of periodic functions. - German Dzyubenko; Victoria Voloshyna; Lyudmyla Yushchenko (J. Approx. Theory, 2021)

Onesided, intertwining, positive and copositive polynomial approximation with interpolatory constraints. - German Dzyubenko; Kirill A. Kopotun (J. Approx. Theory, 2024)