I owe a great debt of gratitude to Martin Hirt. He always had time for me and taught me in endless, but enlightening discussions how to transform cool ideas into presentable results. His support and patience were a great help in reaching this point. I would also like to thank him for organizing the applied geometry seminar 1 . Sincere thanks go to Jesper Buus Nielsen for kindly agreeing to serve as a co-examiner on my committee. I thank all my collaborators on projects both in and outside the scope of this thesis -