The Baima spoken in Jiuzhaigou and surrounding areas differs from that spoken in Songpan County in the Aba Tibetan-Qiang Autonomous Prefecture and Wenxian County in Gansu Province. Sun Hongkai, et al. (2007) document the following three dialects of Baima. The classification of Baima has caused controversy among linguists. Baima is provisionally classified with the Khams group, although it also has a number of Amdo characteristics. Reasons for this are presumably the drastic simplification of the syllable structure, the elimination of ancient Tibetan syllables codas and the presence of tones. While many scholars believe that Baima is a separate Tibeto-Burma subgroup in its own right, others believe that it should be identified as a Tibetan dialect. While Baima and Tibetan share many basic similarities, they are essentially different. In fact, the differences between Baima and Tibetan far exceeded those existing between the three main Tibetan dialects spoken within Chinese territory. Therefore, Baima scholar, Sun Hognkai, argued that "Baima should be considered an independent language which is different from Tibetan but which belongs to the Tibetan branch." Overall, Baima vocabulary is highly heterogeneous. It consists predominantly of transparent Tibetan provenance and appears to combine features of Khams and Amdo. However, sound correspondences between sound system of ancient Tibetan, as reflected in standard Written Tibetan orthography and Baima are less regular than those between Written Tibetan orthography and established groups of Modern Tibetan dialects. Baima vocabulary also exhibits two features which are not present in all other dialects: first, voicing of voiceless aspirated stops and affricates after nasal prefixes; second, the treatment of written Tibetan orthography. Further more, Baima has some words that are of unclear etymology, even in its basic vocabulary. The proportion of these words has never been estimated, nor has basic vocabulary ever been the topic of detailed investigation. In Ekaterina Chirkova's article, "On the Position of Baima within Tibetan: A Look from Basic Vocabulary", she examined the 100-word Swadesh list for Baima, as the layer of lexicon which is arguably least resistible to change and which therefore can shed light on the genetic affiliation of this language. She then discovered that the 100-word Swadesh list for Báimǎ contains 84 words of Tibetan origin, 15 words of unclear origin and another 7 words with partial cognation, in which one element is of unidentified origin. 4 words are doublets, most of which combine one word of unclear origin with a word of Tibetan origin.