On a certain operator that preserves the sign of a function and of its derivatives

Dumitru Ripeanu (Ripianu)
Institutul de Calcul

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D. Ripeanu (Ripianu), On a certain operator that preserves the sign of a function and of its derivatives. (Romanian) Rev. Anal. Numer. Teoria Aproximaţiei, 2 (1973), 105–111.

https://ictp.acad.ro/ranta-ro-72-74/journal/article/view/24/24

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