In the Nyingma tradition, the path of meditation practice is divided into further stages, such as Kriya yoga, Upa yoga, Yoga yana, Mahā yoga, Anu yoga and Ati yoga. The Sarma traditions also include Kriya, Upa (called "Charya"), and Yoga, with the Anuttara yoga class substituting for Mahayoga and Atiyoga. Zen, the name of which derives from the Sanskrit "dhyāna" via the Chinese "ch'an" is a form of Mahayana Buddhism. Yoga practices integrally exist within the Zen Buddhist school. The earliest references to hatha yoga are in Buddhist works dating from the eighth century. The earliest definition of hatha yoga is found in the 11th century Buddhist text "Vimalaprabha", which defines it in relation to the center channel, bindu etc. Hatha yoga synthesizes elements of Patanjali's "Yoga Sutras" with posture and breathing exercises. It marks the development of asanas (plural) into the full body 'postures' now in popular usage and, along with its many modern variations, is the style that many people associate with the word "yoga" today. Various yogic groups had become prominent in Punjab in the 15th and 16th century, when Sikhism was in its nascent stage. Compositions of Guru Nanak, the founder of Sikhism, describe many dialogues he had with Jogis, a Hindu community which practiced yoga. Guru Nanak rejected the austerities, rites and rituals connected with Hatha Yoga. He propounded the path of Sahaja yoga or Nama yoga (meditation on "the name") instead. The "Guru Granth Sahib" states:  Yoga came to the attention of an educated western public in the mid-19th century along with other topics of Indian philosophy. In the context of this budding interest, N. C. Paul published his "Treatise on Yoga Philosophy" in 1851. The first Hindu teacher to actively advocate and disseminate aspects of yoga, not including asanas, to a western audience, Swami Vivekananda, toured Europe and the United States in the 1890s. The reception which Swami Vivekananda received built on the active interest of intellectuals, in particular the New England Transcendentalists, among them Ralph Waldo Emerson (1803–1882), who drew on German Romanticism and philosophers and scholars like G. W. F. Hegel (1770–1831), the brothers August Wilhelm Schlegel (1767–1845) and Karl Wilhelm Friedrich Schlegel (1772–1829), Max Mueller (1823–1900), Arthur Schopenhauer (1788–1860), and others who had (to varying degrees) interests in things Indian.