Article 7(1) of that directive governs the right of residence for a period of more than three months of Union citizens in a Member State of which they are not nationals in the following terms: ‘All Union citizens shall have the right of residence on the territory of another Member State for a period of longer than three months if they: (a) are workers or self-employed persons in the host Member State; or (b) have sufficient resources for themselves and their family members not to become a burden on the social assistance system of the host Member State during their period of residence and have comprehensive sickness insurance cover in the host Member State; or (c) – are enrolled at a private or public establishment, accredited or financed by the host Member State on the basis of its legislation or administrative practice, for the principal purpose of following a course of study, including vocational training; and – have comprehensive sickness insurance cover in the host Member State and assure the relevant national authority, by means of a declaration or by such equivalent means as they may choose, that they have sufficient resources for themselves and their family members not to become a burden on the social assistance system of the host Member State during their period of residence; or …’.