definiens: means any challenge in a legal or administrative proceeding to the patentability, validity, ownership or enforceab ility of any of the Silence Background Patents, Silence Research Pa tents, or Joint Research Patents ( or any claim thereof ), including by : ( x ) filing or pursuing a de claratory judgment action in which any of the Silence Background Patents, Silence Research Patent s, or Joint Research Patents is alleged to be invalid or unenforceable ; ( y ) citing prior art agai nst any of the Silence Background Patents, Silence Research Patents, or Joint Research Patents ( other than art required to be cited by Applicable Law, including under a duty of candor to a patent office ), filing a request for or pursuing a re - examinatio n of any of the Silence Background Patents, Silence R esearch Patents, or Joint Research Patents ( other than with Silence ’s written agreement ), or becoming a party to or pursuing an interference ; or ( z ) filing or pursuing any opposition, cancellation, nu llity, or other like proceedings against any of the Silence Background Patents, Silence Research Patent s, or Joint Research Patents ; but excluding any challenge raised as a defense against a claim, acti on, or proceeding asserted by Silence or its Affiliates against [COMPANY] or its Affiliates o r Sublicensees and excluding any activities conducted by [COMPANY] in the prosecution of Pro duct Specific Patents and, if applicable, other Silence Research Patents or Joint Research Patents, so long as such prosecution is conducted in good faith and in accordance with the applicable provisi ons of this Agreement