Gunzert, R. (1960). Was ist Konzentration? Knapp.
Citazione stile Chigago Style (17a edizione)Gunzert, Rudolf. Was Ist Konzentration? Frankfurt am Main: Knapp, 1960.
Citatione MLA (8a ed.)Gunzert, Rudolf. Was Ist Konzentration? Knapp, 1960.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.