(court-ordered joint parenting agreement governed petitioners' illegitimate son; petitioners did not live together during year in issue but, mother had custody and father had visitation rights and was required to pay child support; dependency exemption altered between parents from year-to-year, but father's deductions dependent on paying child support; mother did not sign court order and father files return without Form 8332; mother signs form 8332 four years later; IRS denied dependency exemption for father because he was a non-custodial parent that failed to attach Form 8332 to the return; court agreed with IRS - no deductions or credits for the father).