++++ SOCIAL SECURITY FOR MIGRANT WORKERS - OLD-AGE PENSIONS - RIGHT ACQUIRED BY VIRTUE OF INSURANCE PERIODS COMPLETED UNDER THE LEGISLATION OF A SINGLE MEMBER STATE - REDUCTION BY MEANS OF AGGREGATION AND PRO RATA CALCULATION - PROHIBITED EXCEPT IN THE CASE OF OVERLAPPING OF BENEFITS FOR THE SAME PERIOD ( REGULATION NO 3 OF THE COUNCIL, ARTICLES 27 AND 28 )