Popoviciu, Elena. “ Essai Concernant Une Analyse Qualitive Bernsteinienne: Essay on a Bernsteinian Qualitative Analysis”. Rev. Anal. Numér. Théor. Approx., vol. 27, no. 2, Aug. 1998, pp. 331-8, https://ictp.acad.ro/jnaat/journal/article/view/1998-vol27-no2-art14.