A Korovkin-type theorem for generalizations of Boolean sum operators and approximation by trigonometric pseudopolynomials
C. Badea, I.A. Badea, C. Cottin, Revue d’Analyse Numérique et de La Théorie de l’Approximation 17 (1988) 7–17.

Quantitative Aussagen zur Blending-Typ-Approximation
C. Cottin, Quantitative Aussagen zur Blending-Typ-Approximation, 1988.

Notes on degree of approximation of B-continuous and B-differentiable functions.
C. Badea, I. Badea, C. Cottin, H.H. Gonska, Journal of Approximation Theory and Its Applications 4 (1988) 95–108.

A note on construction of preconditioners in solving 3D elliptic problems by substructuring
P.S. Vassilevski, S. Petrova, Comptes Rendus de l’Academie Bulgare Des Sciences 41 (1988) 33–36.