The doctrine of patent assignor estoppel is not found in the U.S. statute, but that omission has led to only limited litigation over the doctrine despite the notoriety of the case of Hologic v. Minerva. Nonetheless, the Federal Circuit reinforced the understanding that an assigned patent is still in force when the disputed claim is not seen has having been materially broadened by the time a patent has been granted in its final form, thus closing one of the principal contractual questions surrounding patents that are handed off from one device maker to another.