They occur in Tibetan writing only where one of the vowels i, o, u have to be added to a word ending with an other vowel (s. 15.1, 33.1, 45.2). These additional vowels are then are then always written 'i, 'o, 'u, never 'i etc. (cf. 3.3); and the combinations ai, oi, ui (as in bka'i, mgo'i, bu'i) are pronounced very much like ae, oe, ue, so that the syllables na'i, she'i, ri'i, cho'i, lu'i can only in some vulgar dialects be distinguished from those mentioned in 5.4.
The others ao, eo, io, oo, uo, au, eu, iu (bka'o, bgyi'o, 'gro'o, 'du'o, ga'u, bye'u, khyi'u) are pronounced in rapid conjunction, but either vowel is distinctly audible. In prosody they are generally regarded as one syllable, but if the verse should require it they may be counted as two.
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