definiens: means any challenge in a legal or administrative proceeding to the patentability, validity orenforceability of any of the Patent Rights ( or any claim thereof ), including by : ( a ) filing or pursuing adeclaratory judgment action in which any of the Patent Rights is alleged to be invalid orunenforceable ; ( b ) citing prior art against any of the Patent Rights, filing a request for or pursuing a re - examination of any of the Patent Rights ( other than with COH ’s written agreement ), or voluntarilybecoming a party to or pursuing an interference ; or ( c ) filing or pursuing any re - examination, opposition, cancellation, nullity or other like proceedings against any of the Patent Rights ; butexcluding any challenge raised as a defense against a claim, action or proceeding asserted by COHagainst Licensee, its Affiliates,21Sublicensees, or any downstream customers or users of any Licensed Products or LicensedServices