Monophthongization of -Vu- before labial in Greek

As observed by Hyllested and Cohen (2007), no inherited Greek lexeme contains an initial sequence εὐ-, αὐ-, οὐ- followed by a labial consonant; this leads the authors to propose a sound change which operated in the early stages of Greek: *Vu̯ > ŭ /#_C[+lab], which explains forms such as ὑφαίνω ‘weave’ for expected †αὐφαίνω < *h₂(e)ubʰ-n̥ie̯ /o-. The authors propose that a similar rule might have operated in word-internal position, citing the family of κῡφός ‘hunchbacked’ < *keu̯bʰ-. In the present paper, I will seek to evaluate the claims of Hyllested and Cohen (2007). A discussion of κῡφός and a critical investigation of the possible counterevidence leads to the preliminary conclusion that nothing speaks against the existence of a rule *Vu̯ > ū /C_C[+lab]. After this, I gather additional possible examples of this rule and discuss each instance in detail. The evidence is found to strongly support the proposed rule.