Substantial question of law: High Court appeal admissible only if such question is involved, subject to time and procedural limits. Appeal to the High Court lies only where a substantial question of law arises from an Appellate Tribunal order; certain disputes (including differences over intra State/inter State treatment and place of supply between States or State and Centre) are excluded. Appeals must be filed within one hundred and eighty days with prescribed fee and a memorandum stating the substantial question, though the High Court may admit late filings for sufficient cause. The Court formulates the question, hears the appeal on that question (but may, for reasons recorded, hear other substantial questions), decides and gives reasons, may determine issues not or wrongly decided by the Tribunal, and applies Code of Civil Procedure appeal provisions as far as practicable.