97 STAT. 86 PUBLIC LAW 98-21—APR. 20, 1983 105(a) to the extent such amount constitutes wages (or payments in lieu of wages) for the period during which the individual is absent from work on account of per- manent and total disability. "(3) REDUCTION.— "(A) IN GENERAL.— The reduction under this paragraph is an amount equal to the sum of the amounts received by the individual (or, in the case of a joint return, by either spouse) as a pension or annuity or as a disability benefit— "(i) which is excluded from gross income and payable under— 42 USC 401. "(I) title II of the Social Security Act, 45 USC 23it. "(II) the Railroad Retirement Act of 1974, or "(in) a law administered by the Veterans' Ad- ministration, or "(ii) which is excluded from gross income under any provision of law not contained in this title. No reduction shall be made under clause (i)(III) for any 26 USC 104. amount described in section 104(a)(4). "(B) TREATMENT OF CERTAIN WORKMEN'S COMPENSATION BENEFITS.—For purposos of subparagraph (A), any amount Ante, p. 80. treated as a social security benefit under section 86(d)(3) shall be treated as a disability benefit received under title II of the Social Security Act. " (d) LIMITATIONS.— "(1) ADJUSTED GROSS INCOME LIMITATION.—If the adjusted gross income of the taxpayer exceeds— "(A) $7,500 in the case of a single individual, "(B) $10,000 in the case of a joint return, or "(C) $5,000 in the case of a married individual filing a separate return, the section 37 amount shall be reduced by one-half of the excess of the adjusted gross income over $7,500, $10,000, or $5,000, as the case may be. "(2) LIMITATION BASED ON AMOUNT OP TAX. — The amount of the credit allowed by this section for the taxable year shall not exceed the amount of the tax imposed by this chapter for such taxable year. "(e) DEFINITIONS AND SPECIAL RULES. — For purposes of this sec- tion— "(1) MARRIED COUPLE MUST FILE JOINT RETURN.— Except in the case of a husband and wife who live apart at all times during the taxable year, if the taxpayer is married at the close of the taxable year, the credit provided by this section shall be allowed only if the taxpayer and his spouse file a joint return for the taxable year. "(2) MARITAL STATUS.—Marital status shall be determined under section 143. " (3) PERMANENT AND TOTAL DISABILITY DEFINED.—An individ- ual is permanently and totally disabled if he is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or which has lasted or can be expected to last for a continuous period of not less than 12 months. An individual shall not be considered to be perma- nently and totally disabled unless he furnishes proof of the
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