In its open improvisations, lapidary lyrics, errant melodies, and relentless pursuit of spontaneity, the British experimental band Henry Cow pushed rock music to its limits. Its rotating personnel, sprung from rock, free jazz, and orchestral worlds, synthesized a distinct sound that troubled genre lines, and with this musical diversity came a mixed politics, including Maoism, communism, feminism, and Italian Marxism. In Henry Cow: The World Is...