Does constitutional federalism require a federal court that confronts an outcome-determinative and unresolved State law issue that is particularly within the expertise of a State court—here, whether railroad deeds created an easement or fee simple title, a question antecedent to Petitioners' Fifth Amendment takings claim—to certify the question of State law to the State's highest court rather than making an Erie guess about how the State's highest court would decide the issue?

Under what standards may a federal court make an Erie-guess about how the State's highest court would decide an outcome-determinative issue?

Does constitutional federalism require certification of state law issue?