R -sequence and applications. Andrica, Dorin, Piticari, Mihai (2002) Acta Universitatis Apulensis. Mathematics - Informatics
Remarks on I -density and I -approximately continuous functions Poreda, W., Elzbieta Wagner-Bojakowska, Władysław Wilczyński (1985) Commentationes Mathematicae Universitatis Carolinae