An exceptional teacher-student relationship. Luigi Nono and Helmut Lachenmann were bound by an exceptional teacher-student relationship. The 21-year-old student Lachenmann was so impressed by the charismatic avant-garde composer Nono in Darmstadt in 1957 that he went to Venice to study with him. Lachenmann later designated their relationship as "steering among cliffs" with an intensive exchange of ideas, plans and compositions, personal, and artistic crises as well as heated to controversies which led to quarrels, to a silence of several years, and, finally, to a lasting friendship. This is a document in letter dedications, semester reports and lecture texts that are published here for the first time and presented in their proper context.