What constitutes a structural amendment to a criminal charge?

observed that "[c]onstructive amendment occurs when the terms of the indictment are in effect altered by the presentation of evidence and jury instructions which so modify essential elements of the offense charged that there is a substantial likelihood that the defendant may have been convicted of an offense other than that charged in the indictment." United States v. Wallace, 59 F.3d 333, 337 (2d Cir. 1995) (internal quotation marks omitted). The critical determination is whether the allegations and the proof "substantially correspond." Patino, 962 F.2d at 266 (internal quotation marks omitted).