o. Furthermore, a distributional analysis shows that /o/ tends to occur mainly after another /o/, and only rarely after the other vowels. Vowel length is contrastive in Koti, except in word-final position. Long vowels are best treated as two tone-bearing units. Several vowel coalescence processes do take place, within words as well as across morpheme boundaries: mathápá mawíxí apa → mathápá mawíx'áapa 'these green leaves' (the apostrophe shows the location of coalescence). In case of word-final 'i' it is sometimes accompanied with glide formation: olíli áka → olíly'aáka 'my bed'. Consonants The table below shows the consonant inventory of Koti. The two glides w and y are only phonemically contrastive in certain contexts; in some other contexts, they can be derived from vowels. Consonants in parentheses are extremely rare, with the only example of dh in S&M's corpus, adhuhuri 'second prayer in the morning', being in variation with aduhuri; the fricative zh occurs only in some recent loans from Portuguese. Voiced stops are rather infrequent overall, and they tend to occur after a homorganic, tone-bearing nasal. Additionally, voiced stops often vary with their voiceless unaspirated counterparts. Words in Koti show incompatibility of aspirated consonants; this phenomenon is dubbed Katupha's Law in Schadeberg (1999), and is found in related Makhuwa languages as well. If two aspirated consonants are brought together in one stem, the first such consonant loses its aspiration. The effect is particularly clear in reduplicated words: kopikophi 'eyelash'; piriphiri 'pepper' (cf. Swahili 'piripiri'); okukuttha 'to wipe'. Another incompatibility concerns dental and retroflex consonants, which never occur together within a stem, and usually assimilate when brought together. Consider the class 1 demonstrative for example: o-tthu-o-tu becomes othuutu under influence of the dentral-retroflex incompatibility. Tone Koti, like most Bantu languages, is a register tone language with two tones: High and Low. Tone is not lexically distinctive for verbs, but it is very important in verbal inflection and in some other parts of grammar. Contour tones (falling and rising tones) do occur, but only on long vowels, therefore they are analysed as sequences of the H and L level tones. There is a process of High Doubling which spreads any H tone to the following tone bearing unit, and a process of Final Lowering which deletes any utterance-final High tone. Both can be seen in effect in the following example (Low tone is unmarked): kaláwa 'boat', kaláwá khuúlu 'the biggest boat'. In