Since u-mutation (or u-umlaut) is not the same as a-mutation (or a-umlaut), there is no reason to redirect the former to the latter. I have therefore removed the redirect.
There certanly should be an article on (germanic) u-mutation, the prossess where an a in an earlier syllabel is changed to an "o with a twig" by an u in a later syllabel, as happend in Proto-Norse and Old Norse, especially it's the western varities. The results are still found in especially Icelendic and Faroese, to a lesser degree in Norwegian, and even less in Swedish and Danish. Unfortunatley I don't feel competent to write such an article myself. --188.8.131.52 (talk) 05:26, 20 June 2008 (UTC)