1. Jia-ding Cao, H. H. Gonska,Approximation by Boolean sums of positive linear operators, Rend. Mat. 6, No. 4 (1986), 525–546.
2. Jia-ding Cao, H. H. Gonska,Approximation by Boolean sums of positive linear operators II: Gopengauz-type estimates, J. Approx. Theory 57 (1989), 77–89.
3. Jia-ding Cao, H. H. Gonska,Pointwise estimates for modified linear operators, Portugal. Math. 46 (1989), 401–430.
4. Jia-ding Cao, H. H. Gonska,Approximation by Boolean sums of positive linear operators IV: shape preservation by DeVore-Gopengauz-type approximants, Schriftenreihe des Instituts für Angewandte Informatik, SIAI-EBS-2-92, European Business School 1992.
5. H. Cartan,Elementare Theorie der analytischen Funktionen einer oder mehrer komplexen veränderlichen (1966), Bibliographisches Institut, Mannheim.