Controversial Catholic theologian Rev. Fr. Hans Küng, professor of ecumenical theology at the University of Tübingen, Germany, lectured on "The Problems and Future of the Church." Among Fr. Küng’s struggles with Catholic hierarchy was his reasoned rejection of the doctrine of papal infallibility, which became widely known through his book, Infallible? An Inquiry (1971). Because of Kung's rejection of the doctrine, part of the official teaching of the Catholic Church since 1871, Pope John Paul II revoked Küng's missio canonica in 1979, stripping him of his right to teach in any Catholic institution in Germany.