The frequency count used by Clahsen and Rothweiler, that of Ruoff [Ruoff, A., 1990, “Häufigkeitswörterbuch gesprochener Sprache”, Niemeyer, Tübingen], also gives a count of "Grundverben" - that is, the base verbs, in which all instances of a verb, with and without separable prefixes, are counted as one type. - Bybee (2004), a pag.52