OPINION — AG — SUBSEQUENT TO JANUARY 1, 1981, THE EFFECTIVE DATE OF 68 O.S. 1980 Supp., 2358 [68-2358](10), RETIREMENT BENEFITS NOT TO EXCEED FOUR THOUSAND ($4,000) DOLLARS RECEIVED BY AN INDIVIDUAL FROM THE CIVIL SERVICE OF THE UNITED STATES ARE EXEMPT FROM OKLAHOMA TAXABLE INCOME. (REVENUE AND TAXATION, INCOME TAX, SCHOOLS, TEACHERS RETIREMENT SYSTEM, STATE OFFICERS AND EMPLOYEES) CITE: 70 O.S. 1971, 17-109 [70-17-109], 74 O.S. 1971 923 [74-923] (MICHAEL C. CONAWAY)