Carrier selection 53. (1) The Authority shall ensure that carrier selection is introduced in the call-by-call form, as a minimum, in order to establish effective competition and allow consumers to choose their local-loop operator freely and have access to the services of an alternative operator. (2) The selection possibility shall be offered by all operators having significant market power who must be invited to undertake the technical changes that are necessary to adapt their automatic exchanges so as to be able to offer, in the initial phase, call-by-call selection service which shall be included in the reference interconnect offer. (3) The Authority shall assign prefixes to operators who fall within the category of carriers and take decisions on(a) type of carrier selection; (b) operators eligible to act as carriers; (c) operators subject to the obligation to offer carrier selection; (d) types of calls carried; (e) problems involved in carrier selection such as invoicing and calling line identification; and (f) unfair competition "slamming". Infrastructure sharing issues, such as, 54. (1) The Authority shall encourage infrastructure sharing and ensure that sharing between the operators of public communication networks takes place under conditions of fairness, nondiscrimination and equality of access. (2) The Authority, in consultation with other stakeholders, shall elaborate a procedure for handling relations between the operators of public networks in the matter of the conditions and the sharing of 74