that sort of inconsistency is simply a possibility in any lawsuit based on diversity jurisdiction. It is an elementary rule of federal civil procedure that when a federal court sits in diversity, it must apply state substantive law and federal procedural law. Erie R.R. v. Tompkins, 304 U.S. 64, 78, 58 S.Ct. 817, 82 L.Ed. 1188 (1938). The Erie rule does not change when there is a putative class action. See Shady Grove Orthopedic Assocs., P.A. v. Allstate Ins. Co., 559 U.S. 393, 400, 130 S.Ct. 1431, 176 L.Ed.2d 311 (2010) (“Rule 23 automatically applies ‘in all civil actions and proceedings in the United States district courts.’ ” (quoting Fed.R.Civ.P. 1)). This remains true even when the underlying substantive rule explicitly prohibits class actions. See id. at 398-401, 130 S.Ct. 1431 (<HOLDING>). Therefore, if EU 261 were cognizable in a
holding that even if a defendant in a proposed class action does not seriously contest whether the rule 23 requirements have been met a court nevertheless has the responsibility of conducting its own inquiry as to whether the requirements of rule 23 have been satisfied in a particular case holding that where the action was filed as a class action and a consent decree was entered into entry of the consent decree was sufficient certification of the action as a class action under rule 23 holding that tolling applies to a subsequent class action when the prior denial of class certification was based solely on rule 23 deficiencies of the putative representative holding that rule 23 applied even when the new york statute providing the cause of action prohibited class relief holding that in the rule 23 class action context named plaintiff may appeal a denial of class certification even if his or her individual claims had been satisfied through the entry of judgment