According to the doctrine declared in the Gelpcke case, contract rights acquired under a law which has been held constitutional by the state courts will be protected by the federal courts from impairment by a later decision or decisions of those courts, in cases originating or brought into the lower federal courts because of the diversity of the citizenship of the parties litigant. In later cases this rule has been extended to cover cases where contract rights have been acquired under a state law, presumably valid, which have not had their constitutionality affirmed by the state courts.79