OPINION — AG — A FIREFIGHTER IS ENTITLED TO RECEIVE AN ADDITIONAL 2 1/2% OF HIS AVERAGE MONTHLY SALARY ADDED TO HIS RETIREMENT PENSION FOR SERVICE OF A PARTIAL YEAR PURSUANT TO THE TWENTY(20) TO THIRTY(30) YEAR RETIREMENT PROGRAM. THE CALCULATION OF THE NUMBER OF MONTHS WHICH WILL VEST THE ENTITLEMENT PRIOR TO TWELVE(12) MONTHS SERVICE MAY BE DETERMINED BY RULE OR REGULATION OF EACH LOCAL BOARD OF TRUSTEES OF THE FIREMEN'S RELIEF AND PENSION FUND. CITE: 11 O.S. 1977 Supp., 49-118(3) [11-49-118], 11 O.S. 1977 Supp., 49-105 [11-49-105], 11 O.S. 1971 364 [11-364], 11 O.S. 1977 Supp., 49-106 [11-49-106] (CATHERINE GATCHELL NAIFEH)