Graduation theses"verb with separable and / or unseparable
prefixes" deals with verbs with prefix durch-, hinter-, ob-,
über-, um-, unter-, voll-, wider- and wieder, which may be both
separable and unseparable. At some verbs is prefix only
separable and at the others only unseparable. There also exist
some verbs where is the same prefix in both variants. It’s very
difficult to determine exact  rules for separation or
inseparable prefixes, which can lead to doubts or mistakes of
spokesman. In my thesis I describe criteria for separation, let
us say unseparable prefixes, which are in grammar most often
quoted. Criteria, which is mentioned primarily, is accent.
Accented prefix is separable, unstressed prefix is unseparable.
The second criterion is semantics, when grammar revers to
verb’marks specific and abstract meaning. If the verb is used
in specific meaning, prefix is separated, as far as is used in
abstract meaning, prefix is unseparable.The third aspect is
syntactical criterion. At transitive verbs is prefix separable,
at intransitive verbs is unseparable. The last criterion is
frequency of occurrence, when near specific prefixes one from
both variants predominates. I describe most frequent meanings
of single prefixes in my works, I show in some verbs with these
prefixes, their meaning and examples of using.