For submitting your thesis, you need to have two examiners. The first one is Prof. Müller-Birn, and the second examiner is another institute professor. You are free to choose, and you can ask your advisor for advice. Please send a request to the second examiner before submitting the thesis, and ask for support. Add your thesis proposal to this request. Thus, the examiner can make an informed decision. Do not forget to add all information (advisor, first and second examiner) to the title page of your thesis.