Opinion of Mr Advocate General Léger delivered on 27 May 1997. # Finanzamt Osnabrück-Land v Bernhard Langhorst. # Reference for a preliminary ruling: Bundesfinanzhof - Germany. # Value added tax - Interpretation of Articles 21(1)(c) and 22(3)(c) of the Sixth Directive 77/388/EEC - Document serving as an invoice - Credit note issued by the buyer and not contested by the seller as regards the amount of tax shown. # Case C-141/96. Langhorst TITJUR