What is the doctrine of equivalents, and how does it change infringement analysis?

What does the comparison ask?

In Warner-Jenkinson Co. v. Hilton Davis Chemical Co., the Supreme Court required equivalence to be assessed for individual claim elements. The inquiry can consider whether a difference is insubstantial, including function, way, and result where appropriate. It cannot erase a claim element by comparing only the overall products.

How does the prosecution history matter?

Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. explains how a narrowing amendment made to satisfy a Patent Act requirement can create a presumption that the territory between the original and amended claim was surrendered. The opinion also identifies ways to rebut that presumption. The amendment and its reason need review; neither automatic availability nor an absolute bar should be assumed.

What should a demand or response address?

Identify the limitation, the corresponding accused feature, the asserted equivalence, and the relevant evidence. Review the prosecution history alongside that comparison. A statement that the products do the same thing is not enough to resolve the issue.