To be eligible to be elected it is necessary to be of Dutch nationality, to be over eighteen in age and not to have been excluded from the right to vote (Article 56); there are also certain incompatibilities of function (Article 57), the most important of which is that a minister not belonging to a demissionary cabinet cannot be a member of the States General, a stark contrast with the situation in United Kingdom or Germany, but in line with the United States. This principle underlies the political dualism of Dutch politics. The Houses investigate the Letters of Credence of new members, in this case a written affirmation by the central voting office that they have indeed obtained the necessary number of votes. After the investigation new members swear four oaths: the oath of purification, the oath of allegiance to the Constitution and the oath of loyal discharge of their office are demanded by Article 60; the oath of loyalty to King and Statute is demanded by Article 47 of the Statute of the Kingdom, the higher Constitution of the Realm. All other issues pertaining the elections are regulated by formal law; delegation is possible (Article 59).