Definitions and special rules
For purposes of this section—
(1) Married couple must file joint return
(1)Married couple must file joint return∀ 2#
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 7703.
(3)Permanent and total disability defined∀ 3#
An individual 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 permanently and totally disabled unless he furnishes proof of the existence thereof in such form and manner, and at such times, as the Secretary may require.