Special rule for divorced parents, etc.

For purposes of paragraph (1), the requirements described in this paragraph are met with respect to any calendar year if—

(A) the custodial parent signs a written declaration (in such manner and form as the Secretary may by regulations prescribe) that such custodial parent will not claim such child as a dependent for any taxable year beginning in such calendar year, and

(B) the noncustodial parent attaches such written declaration to the noncustodial parent’s return for the taxable year beginning during such calendar year.

(A) In general For purposes of paragraph (1), the requirements described in this paragraph are met with respect to any calendar year if— (i) a qualified pre-1985 instrument between the parents applicable to the taxable year beginning in such calendar year provides that the noncustodial parent shall be entitled to any deduction allowable under section 151 for such child, and (ii) the noncustodial parent provides at least $600 for the support of such child during such calendar year. For purposes of this subparagraph, amounts expended for the support of a child or children shall be treated as received from the noncustodial parent to the extent that such parent provided amounts for such support.

(B) Qualified pre-1985 instrument For purposes of this paragraph, the term “qualified pre-1985 instrument” means any decree of divorce or separate maintenance or written agreement— (i) which is executed before January 1, 1985 , (ii) which on such date contains the provision described in subparagraph (A)(i), and (iii) which is not modified on or after such date in a modification which expressly provides that this paragraph shall not apply to such decree or agreement.

For purposes of this subsection—

(A) Custodial parent The term “custodial parent” means the parent having custody for the greater portion of the calendar year.

(B) Noncustodial parent The term “noncustodial parent” means the parent who is not the custodial parent.

This subsection shall not apply in any case where over one-half of the support of the child is treated as having been received from a taxpayer under the provision of subsection (d)(3).

For purposes of this subsection, in the case of the remarriage of a parent, support of a child received from the parent’s spouse shall be treated as received from the parent.