59. The State considers, more specifically, that the petition is inadmissible because the intention of the petitioners is for the Commission to act as a tribunal of “fourth instance,” for which it lacks competence, since the petitioners challenge a judicial decision issued within the framework of minimum due process guarantees. With respect to this argument, the Commission reiterates what it has established in its jurisprudence, which is that it is not competent to review judgments decided by national courts acting within their jurisdiction and with due process and judicial guarantees. 44 The Commission cannot serve as an appellate court to examine alleged errors of internal law or fact which may have been committed by the domestic courts acting within their jurisdiction. However, within its mandate to ensure the observance of the rights set forth in the American Convention, the Commission is necessarily competent to declare a petition admissible and rule on its merits when it refers to a domestic legal decision ruled in disregard to due process guarantees and in violation of any other right protected by the American Convention. 45 60. According to this doctrine, the Commission notes that in admitting this petition it does not seek to encroach on the jurisdiction of the domestic judicial authorities to determine child custody matters or to examine any errors of fact and law possibly committed by the domestic courts. The Commission will not determine if the Chilean courts applied Chilean procedural law appropriately or on the assessment of evidence, since such matters are in principle reserved to the domestic courts. The only determination that the Commission will make in the merits stage is whether the decision of the Supreme Court Justice of Chile was issued without regard to due process guarantees and in violation of the rights protected by the American Convention. 61. In the admissibility stage the Commission considers that it is not appropriate to determine whether or not the alleged violations occurred. For the purposes of admissibility, the IACHR should determine whether the arguments advanced in the petition state facts that tend to establish violations of the American Convention, as required under Article 47(b) thereof. The standard of assessment is different from the one needed to decide the merits of a petition. At this stage the IACHR must perform a summary prima facie evaluation to examine whether the petition establishes grounds for the apparent or potential violation of a right guaranteed by the American Convention. 46 This determination involves a summary analysis which does not imply a prejudgment or advance opinion on the merits of the matter. The distinction between the examination required for declaring admissibility and that required for determining a violation is reflected in the IACHR's own Rules of Procedure, which clearly differentiate the stages of admissibility and merits. 47 62. The arguments of the petitioners refer to facts, which, if found to be true, could constitute violations of several rights protected by the American Convention at Articles 8(1), 11(2), 17(1), 24 and 25, in connection with articles 1(1) and 2, to the detriment of Ms. Karen Atala and her daughters; as well as an alleged violation of the rights of the child protected by Articles 19 and 17(4), in connection with Article 1(1), with regard to the daughters of Ms. Atala. 63. The Commission finds prima facie that the arguments raise questions related with the right to equal protection recognized in Article 24, which correspond to an analysis in the merits stage. The petitioners allege that the Supreme Court Justice of Chile accorded a different treatment to Ms. Atala and her former spouse in its ruling on the custody of their daughters, in which the sexual orientation of Ms. Atala was the decisive factor in granting permanent custody to the father. They claim that the distinction based on Ms. Atala’s homosexuality in the custody suit was neither objective nor reasonable and it did not have a legitimate purpose, in contravention of international 44 See IACHR, Report 52/02, Case 11.753, Merits, Ramon Martinez Villareal, United States, October 10, 2002, par. 53; Report 39/96, Santiago Marzioni v. Argentina, IACHR, Annual Report 1996, pars. 48 – 51. 45 See IACHR, Report 52/02, Case 11.753, Merits, Ramon Martinez Villareal, United States, October 10, 2002, par. 53; Report 39/96, Santiago Marzioni v. Argentina, IACHR, Annual Report 1996, pars. 48 – 51. 46 See IACHR, Report 128/01, Case 12.367, Herrera and Vargas (“La Nación”), Costa Rica, December 3, 2001, par. 50. 47 See IACHR, Report 31/03, Case 12.195, Mario Alberto Jara Oñate et al., Chile, March 7, 2003. 13