Хатха-йога
Although kundalini developed as a part of tantra side-by-side with hatha yoga through a process of syncretism, Swami Nigamananda (d. 1935) taught a form of "laya yoga," which he insisted was not part of Hatha yoga. Sivananda introduced many readers to "Kundalini Yoga" with his book on the subject in 1935. This book has in-depth details about Kundalini Yoga, and combines laya teachings from older sources, including the "Hathapradipika" and "Sat Cakra Nirupana".