Yesterday, Judge Andrews excluded testimony by an expert that improperly advanced a "practicing the prior art" defense. It has been firmly established that "practicing the prior art" is not a defense to literal infringement, and thus is not a proper subject for expert testimony. It is acceptable, however, for litigants to argue that if a patentee interprets a claim broadly for infringement purposes, the claim will read on the prior art ("that which infringes, if later, would anticipate, if earlier," the corollary of the proverbial "nose of wax" principle that prohibits parties from taking one view of claim scope for infringement purposes and another for invalidity).
