Artikel 51

1. Where the legislation of a Contracting Party makes the acquisition, maintenance or recovery of entitlement to benefits conditional upon the completion of periods of insurance, the institution which applies that legislation shall, to that end, for the purpose of adding periods together, take account, to the extent necessary, of periods of insurance, employment or occupational activity completed under the legislation of any other Contracting Party, as if they were periods of insurance completed under the legislation of the first Party, provided however that, in the case of periods of employment or occupational activity, these periods would have been considered as periods of insurance if they had been completed under the last mentioned legislation.
2. Where the legislation of a Contracting Party makes the entitlement to benefits conditional upon the completion of periods of employment, occupational activity or residence, the institution which applies that legislation shall, to that end, for the purpose of adding periods together, take account, to the extent necessary, of periods of insurance, employment or occupational activity completed under the legislation of any other Contracting Party, as if they were periods of employment, occupational activity or residence completed under the legislation of the first Party.
3. Where the legislation of a Contracting Party makes the provision of certain benefits conditional upon the completion of periods of insurance in an occupation covered by a special scheme, only periods completed under a corresponding scheme, or, failing that, in the same occupation under the legislation of other Contracting Parties, shall be taken into account for the provision of such benefits. If, notwithstanding periods completed in this way, the person concerned does not satisfy the conditions for entitlement to the said benefits, the periods concerned shall be taken into account for the provision of benefits under the general scheme.
4. The application of the provisions of the preceding paragraphs of this Article is subject to the condition that the person concerned was last subject to the legislation of the Contracting Party under which the benefits are claimed, except in the cases referred to in Article 53, paragraph 1, sub-paragraphs (a) (ii) and (b) (ii).