State succession — Principles — Vienna Convention on State Succession in Respect of Treaties, 1978 — Vienna Convention on State Succession in Respect of State Property, Archives and Debts, 1983 — Whether reflecting customary international law — Outcome of succession to be determined by agreement on equitable basis — Refusal of certain successor States to co-operate — Effects — Duty of States concluding agreement on succession — Possibility of counter-measures against States refusing to cooperate — Duties of third States in the event of decision by international organization regarding property on their territory