»The Letting of Real Estate as a Problem of the Fulfillment of Statutory Requirements in the System of Income Taxes. A Value-Oriented Approach to the Specification of Statutory Commercial Elements Using the Example of the Differentiation of Special and Supplementary Services«: The thesis addresses the income tax classification of the letting of real estate as either asset management or a commercial activity. The process of decision-making in practice, which often appears to be very casuistic, is contrasted with a methodical approach, which - by revealing the principles and valuations of income tax law - is intended to lead to consistent results. In doing so, the fundamental findings of legal methodology are elaborated and made fruitful.