Lettera enciclica Laborem exercens - Ioannes Paulus, 2., papa. (OLS)http://ftis/name/51996; Colmegna, Virginio. (OLS)http://ftis/name/75710; Nell-Breuning, Osvald : Von. (OLS)http://ftis/name/66431 (Morcelliana, 1982)