OPINION OF THE COURT
BECKER, Circuit Judge.
This appeal by Odiri Nkofi Bagot (“Ba-got”) from the District Court’s order denying his petition for a writ of habeas corpus in a deportation case requires us to inquire into the matter of “legal custody.” That inquiry will inform our determination as to whether Bagot is correct that Respondents deported him to Guyana illegally, because, having been in his father’s legal custody at the time the father was naturalized, he is [254]*254derivatively a United States citizen. Respondents maintain that, although Bagot lived with his father in New York, á previous New York state divorce decree and form custody order left him in the legal custody of his mother, who was in Guyana at the time and had never been to the United States.
The District Court was confronted, as we are here, with the difficult question of how to define “legal custody” — but the relevant law is almost silent on that definition. Judge Becker, the author of the Opinion of the Court, believes that, as there is “no federal law of domestic relations,” De Sylva v. Ballentine, 351 U.S. 570, 580, 76 S.Ct. 974, 100 L.Ed. 1415 (1956), legal custody depends on state law in the first instance. Having reviewed the New York precedents, he concludes that Bagot was not in his mother’s legal custody under state law. Judges Rosenn and Nygaard would not delve into state law, but would find that no valid decree awarded custody of Bagot to his mother. The panel is unanimous, however, that under the fallback “actual uncontested custody” standard of the immigration laws, see Matter of M — , 3 I. & N. Dec. 850, 1950 WL 6650 (BIA 1950), Bagot was in the legal custody of his father and thus obtained derivative citizenship. We will therefore reverse the order of the District Court and remand with directions to issue the writ.
The Opinion of the Court in this case consists of Parts I, II, III.A, III.B.2, TV, and V of this Opinion. In the remainder of Part III.B, and in Part III.C, Judge Becker, writing only for himself, explores New York’s law of 'legal custody. Although, as will appear, he finds that law inconclusive, he believes that this threshold exercise is compelled both by the reasoning of our sister Courts of Appeals and by basic principles of federalism.
I. Facts and Procedural History
A. Background Facts
The essential facts are not in dispute. Petitioner Odiri Nkofi Bagot was born on March 6,. 1974, in Guyana. His parents, Brian Bagot and Frances Wright, were natives and citizens of Guyana, and had married there in 1971. In 1982, Brian Bagot left his wife and three children in Guyana and emigrated to the United States, settling in Brooklyn, New York.
In 1984, Brian Bagot, acting pro se, sued Frances Wright for divorce in New York City. On August 28, 1984, Justice Jack Turret of the New York County Supreme Court granted the divorce in a two-page form order. The form contained a child custody provision, in which Frances Wright’s name was typed. The custody provision read: “Frances Bagot shall have custody of the child(ren) of the marriage,” and then listed the three children, including Odiri Bagot. The words “shall have custody of the children) of the marriage” were pre-printed on the form; the names of Frances Bagot and the children were filled in. In addition, typed onto the form was the statement “That the Family Court shall be granted concurrent jurisdiction with the Supreme Court with respect to the issues of; support, custody and visitation.” Frances Wright and all three Bagot children were still living in Guyana at that time; it does not appear that they had ever been in the United States at the time of the divorce.
Life in Guyana was apparently difficult for the children, and in 1988 Frances Wright and Brian Bagot agreed that the children would be better off living in New York. Wright therefore agreed to give Brian Bagot custody of, and responsibility for, the children, and to send them to live with him in New York. Frances Wright herself remained in Guyana until October 1995. [255]*255She then went to New York to live with one of her daughters, and became a naturalized U.S. citizen on February 26, 2001.
Brian Bagot, meanwhile, had made arrangements to bring his children to New York. Odiri Bagot arrived in New York on November 16, 1988, as a lawful permanent resident. He was fourteen years old. Odiri Bagot was raised by his father from that time on. He lived with his father in Brooklyn, and attended Erasmus High School there. On December 13, 1991, Brian Bagot became a naturalized United States citizen. At the time, Odiri Bagot was seventeen years old.
B. The Removal Proceedings
On May 14, 1999, in the County Court for Broome County, New York, Odiri Ba-got pled guilty to third-degree attempted criminal sale of a controlled substance (cocaine). Cf. N.Y. Penal Law § 220.39. He received a sentence of three to six years.
On January 24, 2000, while Odiri Bagot was in prison, the Immigration and Naturalization Service (INS) initiated removal proceedings.1 The INS claimed that Ba-got, as a non-citizen lawful permanent resident, was removable under § 237 of the Immigration and Nationality Act (INA) because he had been convicted of an aggravated felony and of a controlled-substance violation.2 An Immigration Judge ordered Bagot removed to the Bahamas or Guyana. Appeal to the Board of Immigration Appeals (BIA) was waived. Bagot was paroled from the New York prison system on November 19, 2002, and was taken into Bureau of Immigration and Customs Enforcement (BICE) custody.
On February 19, 2003, Bagot filed the present petition for habeas corpus in the United States District Court for the Middle District of Pennsylvania, which entered a temporary stay of deportation. Two days after filing his petition, Bagot filed an application for a Certificate of Citizenship, claiming that he was entitled to derivative citizenship based on his father’s naturalization. The INS denied this application on February 26, 2003. The Administrative Appeals Unit denied an appeal. On February 25, 2004, the District Court denied the petition for habeas corpus. Bagot filed a timely notice of appeal on April 23, 2004.
In its February 2004 decision, the District Court lifted its stay of deportation. Prior to briefing in this appeal, Bagot was apparently removed to Guyana.
II. Jurisdiction and Standard of Review
The District Court had jurisdiction in this habeas action pursuant to 28 U.S.C. § 2241. We have appellate jurisdiction to review the District Court’s denial of habeas corpus under 28 U.S.C. §§ 1291 and 2253. See Gerbier v. Holmes, 280 F.3d 297, 302 (3d Cir.2002). Although Bagot has been removed to Guyana, the removal does not moot his appeal. See Chong v. Quarantillo, 264 F.3d 378, 385 (3d Cir.2001). As the facts are not disputed, we review only the legal question whether Ba-got was in the “legal custody” of his father at the time when his father became a naturalized U.S. citizen. This is a question [256]*256of law subject to plenary review. See Gerbier, 280 F.3d at 302.
Several of the arguments that Bagot now presses were not raised, in specific terms, before the District Court. In particular, much turns on Bagot’s contention that the custody award in the 1984 New York divorce judgment was invalid under New, York law, a contention that was raised for the first time on appeal. Respondents claim that this argument is waived, and urge us not to consider it now, pointing out that “[i]t is well established that failure to raise an issue in the district court constitutes a waiver, of the argument” in this Court. Brenner v. Local 514, United Bhd. of Carpenters & Joiners of Am., 927 F.2d 1283, 1298 (3d Cir.1991).
At oral argument, Bagot’s counsel asserted that certain other arguments in the briefing before the District Court, especially the contention that Bagot’s father never lost his parental rights, implicated the question whether the divorce judgment was valid and therefore put that question fairly before the District Court. We are skeptical. “[T]he crucial question regarding waiver is whether [petitioner] presented the argument with sufficient specificity to alert the district court,” Brennan v. Norton, 350 F.3d 399, 418 (3d Cir.2003) (quoting Keenan v. City of Philadelphia, 983 F.2d 459, 471 (3d Cir.1992)), and it is questionable whether Bagot’s general statement that- his father retained custody was enough to inform the District Court of his present argument that the 1984 New York divorce judgment was entered without subject-matter jurisdiction.
However, this conclusion need not be fatal to Bagot’s appeal. This Court has discretionary power to address issues that have been waived. See Keenan, 983 F.2d at 471; id. at 477 (Higginbotham, J., dissenting in part); Loretangeli v. Critelli, 853 F.2d 186, 189-90 n. 5 (3d Cir.1988) (“This court may consider a pure question of law even if not raised below where refusal to reach the issue would result in a miscarriage of justice or where the issue’s resolution is of public importance.”); Selected Risks Ins. Co. v. Bruno, 718 F.2d 67, 69 (3d Cir.1983) (“[I]n the past we have heard issues not raised in the district court when prompted by exceptional circumstances.”. ’(citations omitted)).
We think that this is just such an exceptional case, and that it is therefore appropriate to consider Bagot’s waived arguments on appeal. The argument omitted in the District Court is a pure question of law, and one that is closely related to arguments that Bagot did raise in that court. No additional fact-finding is necessary. As will appear, the proper resolution of the legal question, though not exactly simple, is reasonably certain. And failing to consider Bagot’s arguments would result in the substantial injustice of deporting an American citizen.
III. Legal Standards
Bagot does not dispute that he has committed a removable offense under 8 U.S.C. §§ 1227(a) (2) (A) (iii) and 1227(a)(2)(B)(i). He argues only that he is in fact an American citizen, and therefore not subject to deportation under 8 U.S.C. § 1227. See Acosta v. Gaffney, 558 F.2d 1153, 1158 (3d Cir.1977). This argument is based on the provisions .of the INA that allow children of citizens, in some circumstances, to claim derivative citizenship.
A. Derivative Citizenship
Bagot was not born in the United States and has never been formally naturalized; his citizenship claim is derivative upon his father’s naturalization. The burden of proof of eligibility for citizenship is on the applicant. Berenyi v. District Di[257]*257rector, INS, 385 U.S. 630, 637, 87 S.Ct. 666, 17 L.Ed.2d 656 (1967). All doubts “should be resolved in favor of the United States and against the claimant.” Id. (quoting United States v. Macintosh, 283 U.S. 605, 626, 51 S.Ct. 570, 75 L.Ed. 1302 (1931)).
At the times relevant to this case, the INA’s requirements for derivative citizenship were as follows:
(a) A child born outside of the United States of alien parents ... becomes a citizen of the United States upon the fulfillment of the following conditions:
(1) The naturalization of both parents; or
(2) The naturalization of the surviving parents if one of the parents is deceased; or
(3) The naturalization of the parent having legal custody of the child when there has been a legal separation of the parents or the naturalization of the mother if the child was born out of wedlock and the paternity of the child has not been established by legitimation; and if
(4) Such naturalization takes place while such child is under the age of eighteen years; and
(5)Such child is residing in the United States pursuant to a lawful admission for permanent residence at the time of the naturalization of ... the parent naturalized under clause (2) or (3) of this subsection, or thereafter ■begins to reside permanently in the United States while under the age of eighteen years.
8 U.S.C. § 1432(a) (1999) (emphasis added), repealed by Child Citizenship Act of 2000 (“CCA”), § 103, Pub. L. No. 106-395, 114 Stat. 1631.3 Thus Bagot must prove four essential facts: (1) that his father was naturalized after a legal separation from his mother; (2) that his father was naturalized before he (Odiri Bagot) turned eighteen; (3) that he was residing in the United States as a permanent legal resident at the time of his father’s naturalization; and (4) that his father had legal custody at the time of his (Brian Bagot’s) naturalization. Respondents concede the first three facts. This case therefore turns on whether Brian Bagot had legal custody of Odiri Bagot in December 1991, when he was naturalized.
B. Legal Custody Under the INA4
The natural starting point for defining legal custody as used in § 1432(a) is the INA itself, as “[w]hat is meant by the [258]*258phrase ‘having legal custody of the child’ is, of course, a question of federal statutory interpretation.” Fierro v. Reno, 217 F.3d 1, 3-4 (1st Cir.2000). But the INA does not define the term “legal custody,” and its legislative history is similarly unhelpful on the question. See id. at 4.
There exist two partially competing paradigms of INA legal custody. The first is that adopted by several other Courts of Appeals, which.have looked to state law to decide who has legal custody of a minor for derivative citizenship purposes. The second is that employed by the BIA, which involves, a more-or-less unitary national standard for determining who has such legal custody.
1. The State-Law Paradigm
The leading Court of Appeals case discussing legal custody for § 1432(a) purposes is Fierro v. Reno, supra. The , First Circuit, after recognizing that the issue is one of federal law, nonetheless looked to state law to determine who had legal custody:
Legal relationships between parents and children are typically governed by state law, there being “no federal law of domestic relations.” Accordingly, subject to possible limitations, we think that the requirement of “legal custody” in section 1432 should be taken presumptively to mean legal custody under the law of the state in question.... [TJhis view is consistent with the approach taken in other cases in which a federal statute depends upon relations that are primarily governed by state law.
217 F.3d at 4 (citations omitted) (quoting De Sylva v. Ballentine, 351 U.S. 570, 580, 76 S.Ct. 974, 100 L.Ed. 1415 (1956)). Other courts have found this analysis persuasive. See Tabucbuc v. Ashcroft, 84 Fed Appx. 966, 969 (9th Cir.2004) (unpublished opinion) (“To determine whether [petitioner] was in the legal custody of his father when he immigrated to the United States in 1984, we look presumptively to Hawaii law.” (citing Fierro))-, Bucknor v. Zemski, No. 01-3757, 2002 WL 221540, *4 (E.D.Pa. Feb. 12, 2002) (“This Court agrees [with Fierro ], and to determine whether [petitioner’s] father had legal custody over [him], this Court will apply Pennsylvania state law.”); cf. In re Bulfa-Dadulo, No. A44 273 047, 2004 WL 1059577 (BIA Mar. 16, 2004) (unpublished decision) (citing Fi-erro approvingly, and looking to state law to determine whether parents were “legally separated”).
The Seventh Circuit has come to the same conclusion independently, noting that the INS has regularly referred to state law in deciding legal custody. Wedderburn v. INS, 215 F.3d 795, 799 (7th Cir.2000) (“ ‘Legal custody’ and ‘legal separation of the parents,’ as words in a federal statute, must take their meaning from federal law.... But federal law may point to state (or foreign) law as a rule of decision, and this is how the INS has consistently understood these terms.”).
On the other hand, the Fifth Circuit has declined to defer to state law in defining the analogous term “legal separation” for § 1432(a)(3) purposes. In Nehme v. INS, 252 F.3d 415, 422 (5th Cir.2001), that court held that “in the absence of plain language to the contrary, Congress does not make the application of a federal act dependent on state law.” Nehme cited Fierro and Wedderbum approvingly for the proposition that the definition of “legal separation” is an issue of federal law, but refused to follow their lead in looking to state law to help decide the issue. Finding that the linchpin of the analysis was the need for uniformity across the nation, the Fifth Circuit determined that the question of legal separation was one of federal law, and “rejectfed] any contention that the law of any one state should govern the determination whether an alien child’s parents were ‘legally separated.’ ” Id. at 423-24.
[259]*259The Fifth Circuit therefore arrived at a unitary definition of legal separation. In so doing, it looked to the laws of several states, and to the legislative history of the INA, which “indicates that Congress wanted to ensure that only alien children whose ‘real interests’ were located in America with their custodial parent, and not abroad, should be automatically naturalized.” 252 F.3d at 425. The court therefore concluded that legal separation requires a judicial act to create separation: mere living apart, without a formal separation, does not qualify as legal separation under the INA. See id. at 425-26; see also Brissett v. Ashcroft, 363 F.3d 130, 133-34 (2d Cir.2004) (approving the INS interpretation, following Nehme, that “an informal separation is not sufficient to render the parties legally separated” under § 1432(a)(3)).
Because Nehme is concerned with the concept of legal separation, not legal custody, it is of limited relevance to this case. The policy goal that the Fifth Circuit drew from the INA’s legislative history— ensuring that the child’s “real interests” were with the custodial parent in the United States — is unlikely to be hindered by applying state law definitions of child custody, as those standards typically make reference to the child’s interests. And, because there is “no federal law of domestic relations,” DeSylva, 351 U.S. at 580, 76 S.Ct. 974, I think that it is most appropriate to turn, in the first instance, to state-law definitions of legal custody. I therefore would not extend Nehme to this case; instead, I agree with Fierro and Wedder-bum that it is appropriate to look to state law to define “legal custody” for the purposes of 8 U.S.C. § 1432(a)(3).
2. The BIA Paradigm
The BIA, however, has made its own attempts at defining “legal custody” under the INA. The BIA’s longstanding interpretation of the “legal custody” requirement is set out in Matter of M — , 3 I. & N. Dec. 850, 1950 WL 6650 (BIA 1950). In that case, the BIA interpreted a predecessor statute of § 1432(a)(3), and stated:
It is the view of the [Immigration and Naturalization] Service that, in the absence of judicial determination or judicial or statutory grant of custody in the case of legal separation of the parent [sic] of a person claiming citizenship under section 314(c), the parent having actual uncontested custody is to be regarded as having “legal custody” of the person concerned for the purpose of determining that person’s status under section 314(c).
3 I. & N. Dec. at 856. Thus, Matter of M — , provides a two-step test of legal custody. First, if there is a “judicial determination or judicial or statutory grant of custody,” then the parent to whom custody has been granted has legal custody for INA purposes. Second, if no such determination or grant exists, then the parent in “actual uncontested custody” is deemed to have legal custody.
The Matter of M— test has been cited approvingly by the Seventh Circuit in Wedderbum, supra, 215 F.3d at 797 (citing Matter of M— for the proposition that “one parent’s permanent physical custody with the other’s consent is ‘legal custody’ ”), by a recent unpublished BIA decision, In re Kwe, No. A37 385 667, 2003 WL 23508701 (BIA Dec. 17, 2003) (unpublished decision) (“In the absence of a judicial determination or judicial or statutory grant of custody in a case of a legal separation of the naturalized parent, the parent having actual, uncontested custody is to be regarded as having ‘legal custody’ of the child.”), and by a District Court in this Circuit, Charles v. Reno, 117 F.Supp.2d [260]*260412, 417 (D.N.J.2000). See also Am. Jur.2d Aliens & Citizens § 2883 (2004) (“ ‘Legal custody’ of the child, for purposes of the statute, resides in the parent who has been granted custody of the child by court order or statutory grant, or, in the absence thereof, in the parent having actual uneontested custody of the child.” (footnotes omitted) (citing Matter of M — )).
Matter of M— appears to represent the position of the agencies charged with interpreting the INA. Respondents thus argue that we are bound to give it deference under Chevron, U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984). This proposition is subject to some debate. See Hughes v. Ashcroft, 255 F.3d 752, 757-758 (9th Cir.2001) (finding Chevron deference to the INS inappropriate in determining United States citizenship, because the INA leaves that determination in the hands of the courts). It is not necessary to decide, however, whether the Matter of M— standard is entitled to Chevron deference, both because it is helpful in understanding the meaning of “legal custody,” and because the parties appear to accept its application here.
3. A Framework for INA Legal Custody: Reconciling Fierro and Matter of M—
This leaves a surfeit of standards, as both the Fierro approach (looking to state law to define legal custody) and the Matter of M— test (looking for a decree of custody or, failing that, for “actual uncontested custody”) are helpful. I conclude, however, that these two standards can be reconciled in a straightforward way.5
. The BIA position in Matter of M— is that a “judicial determination or judicial or statutory grant of custody” creates legal custody. These are all matters of state law, as no federal courts or statutes grant child custody. ■ Thus, the first stage of the Matter of M— determination is a matter of state law, consistent with Fierro. If state law provides no answer as to child custody, then federal courts cannot follow Fierro to determine who has legal custody.6 Rather than simply inventing state law, however, the courts can fall back on the second part of the Matter of M— test: if state law does not-fix “legal custody,” then the federal standard of “actual uncontested custody” applies.
Thus, if, for example, a state court has entered a valid decree granting custody of a child to the child’s, father, then the father has “legal custody” of the child. This result follows naturally from both Fierro and Matter of M— (as it is a “judicial determination or judicial ... grant of custody”). Similarly, if (again, for example) there has been no decree, but a state statute pro[261]*261vides that “in the absence of a decree, a child of divorced parents is in the legal custody of whichever parent he resides with,” then courts should follow the state law under both Fierro and Matter of M— (“statutory grant of custody”). And, if state law is silent about legal custody, Fierro is of no help, and we must rely on the Matter of M— fallback of “actual un-eontested custody.”7
In this case, then, I look first at the New York law defining legal custody. Only because that law does not determine who had legal custody of Odiri Bagot do I turn to the Matter of M— standard of actual uncontested custody.
C. Legal Custody Under New York Law
I believe that our first obligation under Fierro is to examine New York law to see whether it clearly determines legal custody. Unfortunately, New York law, like the INA, does not define the term “legal custody.” The New York Domestic Relations Law uses the term repeatedly, but never defines it. Nor does any case from the Court of Appeals, New York’s highest court, define or explicate the phrase. I have found only three cases in which New York courts have given some clues to the state’s definition of “legal custody,” albeit not clear direction. See Otero ex rel. Otero v. State, 159 Misc.2d 35, 602 N.Y.S.2d 501 (1993); Villafane v. Banner, 87 Misc.2d 1037, 387 N.Y.S.2d 183 (N.Y.Sup.Ct.1976); Coveleski v. Coveleski, 93 A.D.2d 924, 462 N.Y.S.2d 330 (N.Y.App.Div.1983). The first two cases were decided in the context of New York Civil Practice Law and Rules (CPLR) 1201, which allows a parent or other person with “legal custody” to bring a suit on behalf of an infant. The Otero and Villafane courts determined legal custody only for the purpose of allowing the alleged custodian to sue on the child’s behalf.
In Otero, the New York Court of Claims, which adjudicates civil suits against state government agencies, refused to allow an incarcerated father to bring a CPLR 1201 suit on behalf of his infant daughter, who was injured while visiting him in prison. The court noted that there was “very little discussion of the term ‘legal custody’ as used in this context. It apparently incorporates both physical custody and, where someone other than a parent has physical custody, a judicial decree awarding custody to that person.” 602 N.Y.S.2d at 502 (citing Villafane, supra, 387 N.Y.S.2d at 184). Finding that an incarcerated parent could not have physical custody, the court ordered the case dismissed unless the daughter’s legal custodian was substituted as plaintiff within sixty days. Id.
[262]*262In Villafane, the Supreme Court of New York County refused to allow a grandmother to bring a CPLR 1201 action on behalf of her infant grandchild. The grandmother had long had “informal custody” of the infant, but the child had never formally been placed in her care. The court determined that, under CPLR 1201, married parents share legal custody, while, if the parents are separated, “[i]t would appear ... that ‘having legal custody’ was intended to designate a person whose custody was formally determined by judicial decree.” 387 N.Y.S.2d at 184. As no such decree gave the grandmother custody, the court stayed the suit pending appointment of a guardian ad litem to litigate on behalf of the infant.
The CPLR 120Í context is tangential here, and I am none' too confident in draw: ing lessons about New York’s law of legal custody from these two cases. I do so only because there are so few relevant sources for that law, and because Otero and Villafane, like the INA, seem motivated by a desire to fix legal custody on the person who represents the real interests of the child, in order to insure that litigation on behalf of the child is actually in his or her interests.8
On the other hand, the third New York case, Coveleski, supra, 93 A.D.2d 924, 462 N.Y.S.2d 330, is more clearly a domestic relations case. Pursuant to a separation agreement, an earlier court order had granted custody of a child to the mother, and required the father to pay child support. The father ended up having physical custody of the child for a significant period, and did not pay child support during that time. The mother sued for the ar-rearages, and the father “argue[d] that he had physical custody of the child during the period in question and not plaintiff and, therefore, he was not required to pay plaintiff child support pursuant to the agreement.” Id. at 924, 462 N.Y.S.2d 330. The Appellate Division disagreed, noting that the separation agreement and judgment of divorce had never been modified, and “consequently legal custody of the child continued throughout in plaintiff.” Id. (emphasis added).
Coveleski is clearly in some tension with Otero’s suggestion that physical custody is a necessary element of legal custody. Given this tension, I think it best to avoid determining whether New York legal custody' law actually requires physical custody, as Bagót urges us to do.
On the other hand, each of these New York cases places some emphasis on deriving legal custody from a judicial decree. While Otero at least suggests that a parent in physical custody may not need a decree to obtain legal custody, Villafane and Cov-eleski seem to require a judicial decree of custody in essentially all cases.
I thus draw only the most limited conclusions from New York law. Taken together Otero, Villafane, and Coveleski make clear that, at a minimum, a valid [263]*263judicial decree phis physical custody will create legal custody under New York law. Under Coveleski, it is quite likely that a valid judicial decree alone will create legal custody in at least some cases, though we need not decide that issue here. However, in the absence of a valid judicial decree of legal custody, matters are much murkier. No New York case appears to find legal custody in a divorced parent who does not have a custody order from a court.
It is not necessary to decide that New York law requires a valid judicial decree to create legal custody. Rather, I conclude only that New York law is not sufficiently clear to fix INA legal custody in the absence of such a decree. Therefore, under Fierro, I look to New York law to see if any court has issued a valid order determining legal custody. In the absence of such an order, and there is none here, I will not attempt to divine what New York courts would do; rather, I will fall back on the “actual uncontested custody” prong of Matter of M —.9
IV. Legal Custody of Bagot in 1991
We now apply the law to the facts of Bagot’s case. We first examine the 1984 divorce judgment that purportedly granted custody of Bagot to his mother. Finding that this decree did not create legal custody, we address the Matter of M— standard of “actual uncontested custody.”
A. New York Legal Custody
The 1984 judgment, on its face, granted a divorce between Brian Bagot and Frances Wright, and granted custody of the children of their marriage to Frances Wright. Bagot argues that this grant of custody was invalid, because the New York court lacked jurisdiction to decide his custody.
1. The Validity of the Decree
There is no question that the New York County Supreme Court had jurisdiction to enter a judgment of divorce between Brian Bagot and Frances Wright. In New York, the Supreme Court can obtain in rem jurisdiction over a marriage if (among other possibilities) either party to the marriage has resided in New York for two years. N.Y. Dom. Rel. Law § 230(5) (2004). But the New York courts have jurisdiction over child custody determinations only if they can meet the higher standards of the Uniform Child Custody Jurisdiction Act (UCCJA), N.Y. Dom. Rel. Law § 75 — d(1) (1999), which we set forth in the margin (and rely upon infra).10 The [264]*264mere fact of divorce jurisdiction does not create child-custody jurisdiction; ■ the requisites for the two types of jurisdiction are different and must be separately satisfied. See, e.g., Foley v. Foley, 170 Misc.2d 87, 649 N.Y.S.2d 999 (N.Y.Sup.Ct.1996); see generally Merril Sobie, Practice Commentary to NY. Dom. Rel. Law § 76, section 2 (2002).
At the time of his parents’. divorce, Ba-got had never set foot in New York, so paragraph (a) of § 75 — d(l), which applies where New York is the child’s “home state,” could not have created jurisdiction. Paragraph (b), which requires a “significant connection” with New York and “substantial evidence” within the state, was similarly inapplicable, again because there is no cqntention that Bagot had ever been to New York to establish such a connection. “Maximum rather than minimum contacts are required,” Vanneck v. Vanneck, 49 N.Y.2d 602, 427 N.Y.S.2d 735, 404 N.E.2d 1278, 1282 (1980), and the legislative intent behind paragraph (b) was “to limit jurisdiction rather than to proliferate it,” id. Paragraph (c), which creates emergency jurisdiction where the child is physically present in New York, was inapplicable because Bagot was not in the state at the time of the disputed custody grant.
This leaves us with paragraph (d), a fallback provision allowing New York to take jurisdiction where no other state has done so and such an exercise of jurisdiction is in the best interests of the child.11 However, we doubt that, a New York court would have assumed jurisdiction over a child who had never set foot in the state, and who lived with his mother in Guyana, on the basis of § 75-d(l)(d). Cf. Sobie, Practice Commentary to N.Y. Dom. Rel. § 75-d, section 4 (1988) (“The possibility of using the [§ 75-d(l)(d) ] provision is fairly remote; examples might include migrant workers, hobos or perhaps members of a circus troop.”). As long as it was not manifestly against Bagot’s best interests to leave Guyana in control of his custody, a New York court would not have taken jurisdiction over his custody under paragraph (d). See Nesa v. Baten, 290 A.D.2d 663, 664, 736 N.Y.S.2d 173 (N.Y.App.Div.2002) (“[I]t is difficult to see how the [Bangladeshi] children’s best interests would be served by having a New York court litigate issues of custody.”).
Even if there was some conceivable way that the New York court could have taken jurisdiction under paragraph (d), such jurisdiction would require findings that it [265]*265was in the best interests of the child. See People ex rel. Bruzzese v. Bruzzese, 70 A.D.2d 957, 958, 417 N.Y.S.2d 763 (N.Y.App.Div.1979). The two-page form order lacks such findings, and provides no reason to believe that the New York court believed that it had § 75 — d(d) jurisdiction over the child custody determination.
Thus there is no real doubt that the New York County Supreme Court lacked jurisdiction to determine Bagot’s custody. The divorce decree appears to have been simply a form order, normally used for instate divorce cases where custody over the children is easily established; the presiding justice presumably did not notice that he was exceeding his jurisdiction, and no one pointed out this error at the time.12
2. The Appropriateness of Reviewing State Judgments in Immigration Proceedings
Respondents contend, however, that this Court should refuse to examine the validity of the New York custody decree now, almost twenty years after that decree was issued. They argue forcefully that the INS’s successor agency should be able to rely on the finality of state custody orders, and that, if immigration petitioners were allowed to mount collateral attacks on such orders, the result would be a heavy burden on the courts and the INS’s successor agency. Courts might, the argument continues, have to look into whether there was proper service of the custody order, whether there was personal jurisdiction over the parties, and whether the custody decision was proper on its merits. Such inquiries would be costly and time-consuming, and might be susceptible to fraud and manipulation.
We share Respondents’ concern for the finality of state-court judgments in immigration proceedings, and we confine our review of the New York court’s custody order to the purely legal question whether, on the undisputed facts presented by this case, that court had subject-matter jurisdiction to issue a custody decree.13 Such a narrow review does not implicate the concerns raised by the Respondents: we need not look into service of process, personal jurisdiction, or the merits of the custody determination; nor must we engage in any fact-finding that could be undermined by a petitioner’s fraud. In this case, however, the predicate facts — that the divorce decree granted custody of Bagot, who had never been in the United States, to his mother — are undisputed, and they lead inevitably to the legal conclusion that the New York Supreme Court lacked subject matter jurisdiction over the custody determination under § 75-d. We feel confident that we can reach this conclusion without entering the thicket that Respondents conjure.
Basic principles of conflict of laws, including New York’s jurisprudence in the area, support our refusal to recognize custody decrees not properly based on subject matter jurisdiction. Under New York law, and the UCCJA as adopted by most states,14 one state need not recognize the [266]*266custody decree of another state “where the decree was not made under factual circumstances meeting the jurisdictional standards of the [UCCJA].” N.Y. Jur. Domestic Relations § 457 & n.21 (citing Wilber v. Buelow, 136 A.D.2d 786, 523 N.Y.S.2d 249 (N.Y.App.Div.1988) (refusing to give full faith and credit to Texas custody decree where Texas court lacked UCCJA jurisdiction)). No state following the UCCJA— including New York — would enforce the custody decree at issue here; we do not believe that a federal court should be bound by a decree that no state would consider binding.
Respondents correctly note that federal courts in immigration cases disfavor collateral attacks on the state convictions that give rise to aggravated-felony removals. See, e.g., Drakes v. INS, 330 F.3d 600 (3d Cir.2003); Giammario v. Hurney, 311 F.2d 285, 287 (3d Cir.1962). But a collateral attack on the merits of a criminal conviction is much more susceptible to the problems posited by the Respondents than is an attack on a custody decree’s subject-matter jurisdiction.
Child custody is a much more fluid affair than is an aggravated felony conviction. Indeed, few things in the law are as ephemeral as a child custody adjudication. To be sure, a state court’s judgment of conviction renders an immigrant a removable aggravated felon; in the normal case, that status is unlikely to change. But see 8 U.S.C. § 1227(a)(2)(A)(v) (authorizing waiver of deportation for certain felons granted a full pardon by the President or a Governor). But a court’s order granting child custody is rarely the final word on the subject; family circumstances constantly change, and family courts throughout the land frequently modify orders for full or partial custody (visitation) to better accommodate the (changing) best interests of the child. See 45 N.Y. Jur.2d Domestic Relations § 501.
Indeed, at oral argument in this case, Respondents conceded that Brian Bagot could have arranged to have the 1984 custody order modified to comport with the reality that he had undisputed physical custody over Odiri Bagot. Our deference to the finality of state criminal convictions is due in part to the fact that they are intended to be final; such deference to the finality of frequently and easily modified state custody determinations would, we think, be misplaced.
We therefore cannot find that Frances Wright had legal custody of Odiri Bagot under New York law. The decree that granted her custody was facially invalid, and no court in New York or anywhere else would defer to it.
B. Actual Uncontested Custody
If no one had legal custody of Bagot under a New York decree, then were are left to the fallback “actual uncontested custody” prong of Matter of M — . That decision makes clear that, where legal custody has not been determined by decree or statute, “the parent having actual uncontested custody is to be regarded as having ‘legal custody’ of the person concerned for the purpose of determining that person’s status under [§ 1432(a)].” 3 I. & N. Dec. at 856. See Part III.B.2, supra. Therefore, if New York law did not fix Bagot’s legal custody, his father had “legal custody” of him for derivative-citizenship purposes if, but only if, he had “actual uncontested custody.”
[267]*267We think it is clear that he did. Brian Bagot had actual physical custody of Odiri Bagot, who lived with him and attended high school in Brooklyn; Frances Wright approved of the arrangement; and no one else seems to have disputed his father’s custody of Bagot at any time. In Matter of M — , a father who took care of his daughter was found to have “legal custody,” based on his “actual uncontested custody,” where he lived with the child and undertook to provide for her, and where the mother consented to his custody.. 3 I. & N. Dec. at 851, 856. Similarly, in Charles, supra, 117 F.Supp.2d at 418, the court found “actual, uncontested custody” where the father had been responsible for the child’s upbringing and the mother had consented to that custody.
In their brief, Respondents suggest that legal custody under the INA requires a court decree, and that, since no decree granted custody to Bagot’s father, he could not have had legal custody. Respondents base this argument on the Fifth Circuit’s conclusion in Nehme, supra, 252 F.3d at 427, that the term “legal separation” in § 1432(a)(3) requires a judicial decree of separation, not just living apart under legal circumstances. See also Brissett v. Ashcroft, 363 F.3d 130, 133-34 (2d Cir.2004). By analogy to Nehme and Brissett, Respondents conclude that a child of divorced parents whose custody has not been determined by a valid court decree is in the joint custody of both of his parents, and therefore cannot meet the requirement of § 1432(a)(3) unless both parents naturalize. Cf. Wedderburn, 215 F.3d at 800 (where parents share custody, both must naturalize to create derivative citizenship).
Respondents cite no authority for the proposition that legal custody, like legal separation, requires a court decree. We think that the two concepts are easily distinguishable, and that there is no inconsistency in requiring a court order for.legal separation while allowing legal custody to be based on the.consent of the parties or on undisputed physical custody. In fact, at oral argument, counsel for Respondents conceded that Matter of M— forecloses the argument that a decree is required to create legal custody: the BIA’s longstanding position is that, in the absence of a decree, the parent with actual uncontested custody has legal custody for INA purposes: See also Bucknor v. Zemski, No. 01-3757, 2002 WL 442861, *2 (E.D.Pa. Mar. 21, 2002) (rejecting the. argument that a court decree is required to establish “legal custody” for derivative-citizenship purposes). ,
Under the Matter of M— standard, Brian Bagot had “actual uncontested custody” of Odiri Bagot after the'latter arrived in the United States in 1988: For INA purposes, therefore, he also had legal custody.
V. Conclusion
We conclude that, when he was naturalized in 1991, Brian Bagot had “legal custody” of Odiri Bagot for the purposes of 8 U.S.C. § 1432(a)(3), because he had actual uncontested custody under Matter of M — . Because the other requisites of § 1432(a) were also met, Odiri Bagot gained derivative United States citizenship when his father was naturalized. As an American citizen, Bagot was not deportable, and we will therefore reverse the order of the District Court and remand the matter with directions to issue a writ of habeas corpus.