Daniels, D. N., & Price, V. A. (2009). The essential enneagram: The definitive personality test and self-discovery guide (Revised and updated.). HarperOne.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रDaniels, David N., और Virginia Ann Price. The Essential Enneagram: The Definitive Personality Test and Self-discovery Guide. Revised and updated. New York: HarperOne, 2009.
एमएलए (8वां संस्करण) प्रशस्ति पत्रDaniels, David N., और Virginia Ann Price. The Essential Enneagram: The Definitive Personality Test and Self-discovery Guide. Revised and updated. HarperOne, 2009.
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