Joined Cases C-393/04 and C-41/05: Judgment of the Court (Second Chamber) of 15 June 2006 (references for a preliminary ruling from the Cour d'appel de Liège (Court of Appeal, Liège ), Tribunal de première instance de Liège (Court of First Instance, Liège) — Air Liquide Industries Belgium SA v Ville de Seraing (C-393/04) and Province de Liège (C-41/05) (State aid — Definition — Exemption from municipal and provincial taxes — Effects of Article 88(3) EC — Charges having equivalent effect — Internal taxation)