Jastrzębska, Ewa, and Paulina Legutko-Kobus. “Initiatives for People Aged 50+ Implemented by Municipalities and Enterprises in the Opole Special Demographic Zone”. Czasopismo "Economics and Environment", vol. 68, no. 1, Jan. 2019, p. 11, https://ekonomiaisrodowisko.pl/journal/article/view/111.