a contract to which any international convention, treaty or agreement specified in that State’s declaration, to which the State is or may become a Contracting State, applies, including any of the conventions referred to in paragraph 1 of this article, even if such State has not excluded the application of paragraph 2 of this article by a declaration made in accordance with article 21. Article 21 Procedure and effects of declarations 1. Declarations under article 17, paragraph 4, article 19, paragraphs 1 and 2, and article 20, paragraphs 2, 3 and 4, may be made at any time. Declarations made at the time of signature are subject to confirmation upon ratification, acceptance or approval. 2. Declarations and their confirmations are to be in writing and to be formally notified to the depositary. 3. A declaration takes effect simultaneously with the entry into force of this Convention in respect of the State concerned. However, a declaration of which the depositary receives formal notification after such entry into force takes effect on the first day of the month following the expiration of six months after the date of its receipt by the depositary. 4. Any State that makes a declaration under this Convention may modify or withdraw it at any time by a formal notification in writing addressed to the depositary. The modification or withdrawal is to take effect on the first day of the notification by the depositary. Article 22 Reservations No reservations may be made under this Convention. Article 23 Entry into force 1. This Convention enters into force on the first day of the month following the expiration of six months after the date of deposit of the third instrument of ratification, acceptance, approval or accession. 2. When a State ratifies, accepts, approves or accedes to this Convention after the deposit of the third instrument of ratification, acceptance, approval or accession, this Convention enters into force in respect of that State on the first day of the month following the expiration of six months after the date of the deposit of its instrument of ratification, acceptance, approval or accession. Article 24 32