A federal statute, 8 U.S.C. § 1409, sets requirements for acquisition of U.S. citizenship by a child born outside the United States to unwed parents, only one of whom is a U.S. citizen. If the mother is the U.S. citizen, the child acquires citizenship at birth. Section 1409(a) states that when the father is the citizen parent, the child acquires citizenship only if, before the child reaches the age of 18, the child is legitimized under the law of the child's residence or domicile, the father acknowledges paternity in writing under oath, or paternity is established by a competent court. Tuan Anh Nguyen was born in Vietnam to a Vietnamese mother and a U.S. citizen father, Joseph Boulais. At six years of age, Nguyen came to the United States, where he became a lawful permanent resident and was raised by his father. When Nguyen was 22, he pleaded guilty in a Texas court to two counts of sexual assault. The U.S. Immigration and Naturalization Service initiated deportation proceedings against Nguyen, and an immigration judge found him deportable. While Nguyen's appeal to the U.S. Board of Immigration Appeals was pending, Boulais obtained from a state court an order of parentage that was based on DNA testing. The board dismissed Nguyen's appeal, denying his citizenship claim on the ground that he had not established compliance with § 1409(a). Nguyen and Boulais appealed to the U.S. Court of Appeals for the Fifth Circuit, which rejected their contention that § 1409 discriminated on the basis of gender and thus violated the Constitution's equal protection guarantee. Was the Fifth Circuit's decision correct?