According to Nataniel Santos Gomes, however, the phonetic inventory of Tupi was simpler: Consonants: p, t, k, ‘ () b () s, x () m, n, ñ () û (), î () r () Vowels i, y (), u, ĩ, ỹ, ũ e, o, õ, ẽ a, ã This scheme does not regard Ŷ as a separate semivowel, does not consider the existence of G (), and does not differentiate between the two types of NG ( and ), probably because it does not regard MB (), ND () and NG () as independent phonemes, but mere combinations of P, T, and K with nasalization. Santos Gomes also remarks that the stop consonants shifted easily to nasal stops, which is attested by the fitful spelling of words like umbu (umu, ubu, umbu, upu, umpu) in the works of the early missionaries and by the surviving dialects. According to most sources, Tupi semivowels were more consonantal than their IPA counterparts. The Î, for instance, was rather fricative, thus resembling a very slight , and Û had a distinct similarity with the voiced stop (possibly via , which would likewise be a fricative counterpart of the labiovelar semivowel), thus being sometimes written gu. As a consequence of that character, Tupi loanwords in Brazilian Portuguese often have j for Î and gu for Û. Writing system It would have been almost impossible to reconstruct the phonology of Tupi if it did not have a wide geographic distribution. The surviving Amazonian Nhengatu and the close Guarani correlates (Mbyá, Nhandéva, Kaiowá and Paraguayan Guarani) provide material that linguistic research can still use for an approximate reconstruction of the language. Scientific reconstruction of Tupi suggests that Anchieta either simplified or overlooked the phonetics of the actual language when he was devising his grammar and his dictionary. The writing system employed by Anchieta is still the basis for most modern scholars. It is easily typed with regular Portuguese or French typewriters and computer keyboards (but not with character sets such as ISO-8859-1, which cannot produce ẽ, ĩ, ũ, ŷ and ỹ). Its key features are: The tilde indicating nasalisation: a → ã. The circumflex accent indicating a semivowel: i → î. The acute accent indicating the stressed syllable: abá. The use of the letter x for the voiceless palatal fricative , a spelling convention common in the languages of the Iberian Peninsula but unusual elsewhere. The use