Horace Gray, New Orleans Water-Works Company v…
“ When the existence and the construction of a contract are undisputed, and the state court upholds a subsequent law, on the ground that it did not impair the obligation of the admitted contract, it is equally clear that this court has jurisdiction. When the state court holds that there was a contract conferring certain rights, and that a subsequent law did not impair those rights, this court has jurisdiction to consider the true construction of the supposed contract ”
