Should Article 2(2), read in combination with Article 4(1), of Council Directive 2000/78/EC 1 of 27 November 2000 establishing a general framework for equal treatment in employment and occupation, be interpreted as precluding provisions of national law which provide that impaired hearing below the prescribed standard constitutes an absolute impediment to work as a prison officer and that the use of corrective aids to assess compliance with the requirements is not permitted?