It also kept the archaic letters digamma () for and qoppa () for . The ratio of observance/neglect of digamma varies between them. Setting in the above formula does not give an integral representation of the digamma function. Digamma or wau is in turn the ancestor of the Latin letter F. Below, is the gamma function and is the digamma function. More explicit, though less precise, estimates may be derived by bounding the digamma function. After sound changes eliminated from spoken Greek, "digamma" was used only as a numeral. A digamma also saved the hiatus in the third foot. Thus "abroutes", may be read as abrouwes (), with tau () replacing a digamma. The digamma has a rational zeta series, given by the Taylor series at . Literary texts in Doric and inscriptions from the Hellenistic age have no digamma. Hesiod does not observe digamma as often as the others do. For digamma, this led to the two main variants of classical "F" and square .