Somewhat intriguing excerpt from yogashikhopaniSat (yoga-shikha-upanishad):
...| Walk through the inner stages of Mantra-, Laya-, Hatha- and Raja-Yoga, ||129|| this is indeed a unique fourfold Maha-Yoga. | Exhale with the sound HA and inhale again with the sound SA, ||130|| this way all living beings do chant the Mantra "hamsa hamsa". | The other way around the Yogi should recite this Mantra – after instruction by his teacher - in the Sushumna. ||131|| "SO-HAM, I am it, ´I am it´ recited this way is called Mantra-Yoga. | Through understanding of the Mantra-Yoga the Yogi will be directly born onto the path of liberation. ||132|| It is said that in the sound HA the sun is contained, in the sound SA the moon. | Hatha-Yoga means uniting of sun and moon. ||133|| When the individual and the universal sould became united, Hatha-Yoga | then swallows the lethargy, the result of the basic characteristics of human beings. ||134|| When the unity is perfected the changeable (Chitta) in the human being is absorbed in the Absolute (Brahma). | The goal of Laya-Yoga will be reached through the resulting rest of the life force (Prana). ||135|| Through the sublime state of Laya bliss will be achieved out of itself. | This is localised in the holy shrine in the middle of the Vagina (Yoni), comparable with the Hibiskus- or Dupurmoni- blossom. ||136|| Hidden in all living beings the essence of the goddess lies dormant as vaginal secretion (Rajas). | Hence it is handed down that Raja-Yoga evolves from the unification of male semen (Retas) and female vaginal secretion (Rajas). ||137|| If Raja-Yoga is reached, supernatural powers (Siddhi) are achievable. | Typical for the fourfold Yoga is always the unification of ascending energy (Prana) with descending energy(Apana). ||138||
