Fletcher YoderA presumption of prosecution history estoppel may be rebutted by a showing of unforeseeability of the alleged equivalent at the time of the narrowing amendment or by a showing of tangentiality of the alleged equivalent with respect to the rationale for the narrowing amendment.
Question of law is presented by issue of whether patentee, having made narrowing claim amendment for substantial reason related to patentability, has successfully rebutted presumption that it has surrendered all territory between original claim limitation and amended limitation, since prosecution history estoppel is equitable in nature, and whether such estoppel applies presents question of law.