definiens: means any challenge to the validity or enforceability of any Patent Right within the [COMPANY] IP or OphthotechCollaboration IP, including any challenge effected by ( i ) filing a declaratory judgment action in which any such PatentRight is alleged to be invalid or unenforceable, ( ii ) citing prior art pursuant to 35 U.S.C. § 301, filing a request for re - examination of any such Patent Right pursuant to 35 U.S.C. § 302 or § 311 or provoking or becoming party to aninterference with an application for any such Patent Right pursuant to 35 U.S.C. § 135, or ( iii ) filing or commencing anyreexamination, opposition, cancellation, nullity or similar proceedings against any such Patent Right in any country, including any such challenge that any Existing Fovista Agreement prohibits [COMPANY] or its Affiliates orSublicensees from initiating or that would give a counterparty to any Existing Fovista Agreement a right to terminate, or otherwise claim a remedy ( e.g