Mahler’s Ninth sings of beauty, love and impermanence “World! Farewell!” noted Mahler above the final measures. His last completed symphony embraces the world of yesterday, while pushing the door wide open to the modern age.

The composition, created in a “mad urgency and haste,” had already posed puzzles for his copyists. While Mahler was able to clarify some of them already in the engraver’s model, others remained unsolved. Performance and printing had to be left to posterity.

The text-cr...