The vowel switches in
the verb-group 4 most
often follow certain patterns. Group 4-verbs with j + long "u" in the imperative,
the present and the infinitive switch to a long "ö" in the preterite and a long
"u" in the supine: (In Swedish you never write "j" between "g" and "ö" or between
"sk" and "ö".)