ARB is the assignee of U.S. Patent No. 5,591,098 (the ‘098 patent), which relates in part to a locking differential and a cylinder means. R&P filed for declaratory judgment that their "Ziplocker" product did not infringe the '098 patent. Previously, the parties (ARB and R&P) had agreed that all elements of the ‘098 patent claims at issue were present in the Ziplocker product except the "cylinder means." The parties also agreed that the cylinder means "would have been foreseeable to a person having ordinary skill in the art at the time the application for the ’098 patent was filed", and that “should the Court hold . . . that foreseeability of an equivalent at the time of application prevents use of the doctrine of equivalents, . . . the accused differential would not infringe under the doctrine of equivalents.”

The district court held that foreseeability of an equivalent at the time of application did not preclude the application of the doctrine of equivalents (DOE). The district court further found that a finding of infringement under DOE would vitiate the "cylinder means" limitation. Therefore, the district court granted summary judgment of non-infringement in favor of R&B.

The Federal Circuit agreed with the district court as far as the DOE not being precluded by foreseeability. In so doing, the Federal Circuit noted that there is no foreseeability limitation on the application on the doctrine of equivalents, and that excluding equivalents that were “foreseeable at the time of patenting” would directly contradict with holdings in which “known interchangeability” was relied upon as a basis for finding infringement under DOE. The Federal Circuit then concluded that the district court had failed to enforce the stipulation entered between the parties as to infringement, finding that the stipulation precluded the conclusion that the claimed “cylinder means” was vitiated. Accordingly, the district court's ruling was reversed and remanded.