3 books • 4 series
Schopenhauer: On the Fourfold Root of the Principle of Sufficient Reason and Other Writings (The Cambridge Edition of the Works of Schopenhauer)
The A to Z of Schopenhauer's Philosophy (The A to Z Guide)
Historical Dictionary of Schopenhauer's Philosophy (Historical Dictionaries of Religions, Philosophies, and Movements) (Historical Dictionaries of Religions, Philosophies, and Move, #55)