in jeans." In September 1968 Adorno went to Vienna for the publication of Alban Berg: Master of the Smallest Link. Upon his return to Frankfurt, events prevented his concentrating upon the book on aesthetics he wished to write: "Valid student claims and dubious actions," he wrote to Marcuse, "are all so mixed up together that all productive work and even sensible thought are scarcely possible any more." After striking students threatened to strip the institute's sociology seminar rooms of their furnishings and equipment, the police were brought in to close the building. Later years Adorno began writing an introduction to a collection of poetry by Rudolf Borchardt, which was connected with a talk entitled "Charmed Language," delivered in Zurich, followed by a talk on aesthetics in Paris where he met Beckett again. Beginning in October 1966, Adorno took up work on Aesthetic Theory. In June 1969 he completed Catchwords: Critical Models. During the winter semester of 1968–69 Adorno was on sabbatical leave from the university and thus able to dedicate himself to the completion of his book of aesthetics. For the summer semester Adorno planned a lecture course entitled "An Introduction to Dialectical Thinking," as well as a seminar on the dialectics of subject and object. But at the first lecture Adorno's attempt to open up the lecture and invite questions whenever they arose degenerated into a disruption from which he quickly fled: after a student wrote on the blackboard "If Adorno is left in peace, capitalism will never cease," three women students approached the lectern, bared their breasts and scattered flower petals over his head. Yet Adorno continued to resist blanket condemnations of the protest movement which would have only strengthened the conservative thesis according to which political irrationalism was the result of Adorno's teaching. After further disruptions to his lectures, Adorno canceled the lectures for the rest of the seminar, continuing only with his philosophy seminar. In the summer of 1969, weary from these activities, Adorno returned once again to Zermatt, Switzerland, at the foot of Matterhorn to restore his strength. On August 6 he died of a heart attack. Intellectual influences Like most theorists of the Frankfurt School, Adorno was influenced by the works of Hegel, Marx and Freud. Their major theories fascinated many left-wing intellectuals in the first half of the 20th century. Lorenz Jäger speaks critically of Adorno's "Achilles' heel" in his political biography: that