the effects of "a"-mutation are perhaps most noticeable in certain verb types, e.g. strong verbs of classes 2, 3 and 4) where "o" in the past participle alternates with "u" in the preterite plural. for example, old english "flogen" "flown" < *"fluganaz" alternated with "flugon" "they flew" < *"flugun". otherwise, where and would originally have alternated morphologically, the old germanic languages had almost always generalised one vowel or the other throughout the paradigm, although there does occur in old swedish (especially in the laws of östergötland) traces of regular alternation between and in line with "a"-mutation, e.g. "kona" (subj.) : "kunu" (obj.) "woman". as can be seen from the examples above, "a"-mutation is also found in lexical alternations.