<Tr> <Td> ⟨ ντ ⟩ </Td> <Td> (d) </Td> <Td> </Td> </Tr> <Tr> <Td> ⟨ τζ ⟩ </Td> <Td> (dz) </Td> <Td> </Td> </Tr> <Tr> <Td> ⟨ τσ ⟩ </Td> <Td> (t͡s) </Td> <Td> </Td> </Tr> <P> In the polytonic orthography traditionally used for ancient Greek, the stressed vowel of each word carries one of three accent marks: either the acute accent (ά), the grave accent (ὰ), or the circumflex accent (α̃ or α̑). These signs were originally designed to mark different forms of the phonological pitch accent in Ancient Greek . By the time their use became conventional and obligatory in Greek writing, in late antiquity, pitch accent was evolving into a single stress accent, and thus the three signs have not corresponded to a phonological distinction in actual speech ever since . In addition to the accent marks, every word - initial vowel must carry either of two so - called "breathing marks": the rough breathing (ἁ), marking an / h / sound at the beginning of a word, or the smooth breathing (ἀ), marking its absence . The letter rho (ρ), although not a vowel, also carries a rough breathing in word - initial position . If a rho was geminated within a word, the first ρ always had the smooth breathing and the second the rough breathing (ῤῥ) leading to the transiliteration rrh . </P>

What letters are not in the greek alphabet