lease, for the first time in his reply brief, thus, he has waived it. In most circumstances a litigant who fails to raise an argument until his reply brief wül be deemed to have waived that argument. Wilson v. O’Leary, 895 F.2d 378, 384 (7th Cir. 1990). This case is before us, however, on a motion for dismissal pursuant to Rule 12(b)(6). The inquiry we are faced with is whether the plaintiff can prove any set of facts to support his allegation. Conley v. Gibson, 355 U.S. 41, 45-46, 78 S.Ct. 99, 101-02, 2 L.Ed.2d 80 (1957). This court has held that when reviewing Rule 12(b)6) motions, we wül consider new factual allegations raised for the first time on appeal provided they are consistent with the complaint. See Hrubec v. National R.R. Passenger Corp., 981 F.2d 962, 963-64 (7th Cir.1992) (<HOLDING>); Dawson v. General Motors Corp., 977 F.2d 369,
holding that a court in deciding a rule 12b6 motion may consider a document that is incorporated by reference into the complaint holding that the essential inquiry in conversion of a rule 12b6 motion to a rule 56 motion is whether the appellant should reasonably have recognized the possibility that the motion might be converted into one for summary judgment or was taken by surprise and deprived of a reasonable opportunity to meet facts outside the pleadings holding that a plaintiff may attempt to survive a rule 12b6 motion by adding essential new facts in a brief on appeal holding that class claims that fail to meet the requirements of rule 23 may be properly dismissed by granting a rule 12b6 motion holding that plaintiff cannot introduce new allegations or new facts in opposition to a motion to dismiss