Dan. [a], [u] became [e], [y] before following [i]; [{au}{C|CC}i] > [{ey}{C|CC}i]

Dan. [a], [u] became [e], [y] before following [i]; [{au}{C|CC}i] > [{ey}{C|CC}i]
There is evidence that Danian underwent i-mutation is some circumstances, notably a change of [a] > [e] in the names Gochressiel from hrassa “precipice” (Ety/KHARÁS) and Denethor from ᴹ✶Ndanithārō (Ety/DAN, LR/188), as well as [u] > [y] in the plural yrc of urc (Ety/ÓROK). These same changes also occurred in Old English and Old Norse, the real-world inspirations of Ossiriandic and East Danian (ref/@@@). It is likely i-mutation occurred for other vowels, but there is not enough evidence to determine what they were.

Phonetic Rule Elements

[aCi] > [eCi]
[aCCi] > [eCCi]
[uCi] > [yCi]
[uCCi] > [yCCi]

Phonetic Rule Examples

ndaniθǭrō > ndeniθǭrō aCi > eCi ᴹ√DAN > Dan. Denethor ✧ Ety/DAN
lugni > lygni uCCi > yCCi ᴹ✶lugni > Dan. lygn ✧ Ety/LUG²