Judgment of the Court (Fifth Chamber) of 11 January 2001 in Case C-464/98 [reference for a preliminary ruling from the Landesgericht für Zivilrechtssachen Wien (Austria)]: Westdeutsche Landesbank Girozentrale v Friedrich Stefan, in the presence of: Republik Österreich (National rules prohibiting the registration of mortgages in foreign currencies — Breach of that prohibition before Community law entered into force in Austria — Interpretation of Article 73b of the EC Treaty (now Article 56 EC) — Whether Community law can operate to remedy the registration)