Once adopted, treaties and their amendments must follow the formal legal procedures of the United Nations, as applied by the Office of Legal Affairs, including signature, ratification and entry into force. Australian contracts generally fall into the following categories: extradition, postal agreements and payment vouchers, trade and international conventions. Contracts sometimes contain provisions relating to self-dismissal, which means that the contract is automatically terminated when certain defined conditions are met. Some contracts are only supposed to be temporarily binding by the parties and expire at some point. Other contracts may self-terminate if the contract exists only under certain conditions. .