“…This concept has been studied even in topological spaces (see e.g. Das, 2012;Das & Ghosal, 2011;Lahiri & Das, 2005;Lahiri & Das, 2007/2008 and in ( )-groups (see also , 2013bBoccuto, Dimitriou, & Papanastassiou, 2010b, 2012a, 2012b, 2012dBoccuto, Dimitriou, Papanastassiou, & Wilczyński, 2012, 2013. This notion has been several applications in the very recent literature.…”