“…Along with various scalarization techniques, generalized vector metrics have been used [15,17,24]. Some authors have considered directional and more general set perturbations [16,18,21,23,[25][26][27][28][29][30][31][32]. Using the latter approach, Bednarczuk and Zagrodny [31] obtained recently an extension of the Borwein-Preiss variational principle to vector-valued functions.…”