or both /i/. The number of Warlpiri roots with adjacent syllables having /u/ and /i/ is very small. Both progressive and regressive vowel harmony occur. In progressive vowel harmony, the second vowel changes to match the first; in regressive harmony, the first changes to match the second. The tendency to prefer adjacent high vowels to be identical also spreads across morpheme boundaries within a word. Adding a suffix to a word can place a /u/ and an /i/ in contact. When that happens, one of the vowels tends to assimilate by changing to match the other vowel. That kind of assimilation is called vowel harmony and is common in the world's languages. It is found, for example, in Finnish, Hungarian, Mongolian and Turkish. Regressive harmony occurs only when a tense suffix is attached to a verb (see below). For example, when the verb (class 2) is placed in the past tense with the suffix , the result is , not . Progressive harmony occurs with most other kinds of suffixes. For example, when the ergative case suffix is attached to the noun 'boomerang', the result is , not . On occasion, long chains of high vowels can assimilate, each forcing the next. For example, when the class 2 verb is attached to the past tense suffix -rnu, the resulting word is . Words No Warlpiri word begins with an alveolar consonant; the first consonant of a word must be bilabial, palatal, retroflex or velar. Exceptions include borrowings such as 'dollar', from English dollar. All Warlpiri words end in vowels. A word whose final meaningful component ends in a consonant is usually "corrected" by appending a meaningless suffix, usually . Alphabet Since the 1950s, Warlpiri has been written in the Latin script using an alphabet originally devised by Lothar Jagst and later modified slightly. The Warlpiri alphabet uses only ordinary letters, with no accent marks, and has the following deviations from IPA: Long vowels are written by doubling the vowel letter: ii, aa, uu. Retroflex consonants are written with digraphs formed by prefixing r to the usual alveolar symbol: rt, rn, rl. The palatal stop is written j. Other palatals are written with digraphs formed by suffixing y to the usual alveolar symbol: ny, ly. The palatal approximant is written y. The velar nasal is written ng. The alveolar trill is written rr. The retroflex flap is written rd. The retroflex