Perhaps you should try some spelling variations:
mittelbar » mittelbare, unmittelbar, ermittelbar
unmittelbare » unmittelbaree, ununmittelbare, unermittelbare, unmittelbar, ermittelbar
vermittelbar » vermittelbare, verunmittelbar, verermittelbar, ermittelbar, vermittelter, vermittelnder

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((mittelbar OR unmittelbare) OR ((unmittelbare OR vermittelbar) OR unmittelbare)).
• Adding a wildcard symbol may retrieve word variants: ((mittelbar or unmittelbare) or ((unmittelbare or vermittelbar) or unmittelbare))*.