In applying the foregoing principles to the taxation of MNEs, one of the most difficult issues that has arisen is the establishment for tax purposes of appropriate transfer prices. Transfer prices are the prices at which an enterprise transfers physical goods and intangible property or provides services to associated enterprises. For purposes of these Guidelines, an “associated enterprise” is an enterprise that satisfies the conditions set forth in Article 9, sub-paragraphs 1a) and 1b) of the OECD Model Tax Convention. Under these conditions, two enterprises are associated if one of the enterprises participates directly or indirectly in the management, control, or capital of the other or if “the same persons participate directly or indirectly in the management, control, or capital” of both enterprises (i.e. if both enterprises are under common control). The issues discussed in these Guidelines also arise in the treatment of permanent establishments as discussed in the Report on the Attribution of Profits to Permanent Establishments that was adopted by the OECD Council in July 2010, which supersedes the OECD Report Model Tax Convention: Attribution of Income to Permanent Establishments (1994). Some relevant discussion may also be found in the OECD Report International Tax Avoidance and Evasion (1987).