(1) an immediate pension if, at the time of cessation,
(a) his age and years of service giving entitlement to a pension total 80 or more, and if he is at least 50 years of age; or
(b) he has attained 60 years of age; or
(2) an annual allowance payable immediately if, at the time he ceases to hold employment, he has reached age 50 and has at least 10 years of service giving entitlement to a pension, and equal to the amount of pension calculated under subdivisions 0.1 and 1 of Chapter V of Title I less the smallest of the 2 products obtained by multiplying 3% of the pension amount
(a) by 60 less his age, rounded to the nearest tenth of a year; or
(b) by half the difference between 80 and the total of his age and years of service giving entitlement to a pension.