Powell, B., & Lawlor, P. (2018). Relentless forward progress: A guide to running ultramarathons (Unabridged.). Tantor Media.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रPowell, Bryon, और Patrick Lawlor. Relentless Forward Progress: A Guide to Running Ultramarathons. Unabridged. Old Saybrook: Tantor Media, 2018.
एमएलए (8वां संस्करण) प्रशस्ति पत्रPowell, Bryon, और Patrick Lawlor. Relentless Forward Progress: A Guide to Running Ultramarathons. Unabridged. Tantor Media, 2018.
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