1) How can a horizontal choice-of-law analysis help in understanding Shady Grove? Imagine that a class action for statutory penaties under Pennsylvania law had been brought in state court in New York. Would section 901 have applied? Imagine that a class action for statutory penaties under New York law had been brought in state court in Pennsylvania. Would section 901 have applied? Is Stevens right that section 901 is procedural for choice-of-law purposes?

2) Is Scalia right that FRCP 23 can apply even if section 901 is understood as substantive? 

3) Is there really any way to tell whether section 901 is substantive or procedural for horizontal choice-of-law purposes? When would a New York state court have occasion to address the matter?

4) What is Ginsburg's argument? Is she saying that section 901 should be used because it is substantive for choice-of-law purposes or because of the twin aims (or both)?