definiens: means any challenge in a legal or administrative proceeding to the patentability, val idity, ownership or enforceability of any of the F -star Patents ( or any claim thereof ), including by : ( i ) filing or pursuing a declaratory judgment action in which any of the F -star Patents or Platform Patents is alleged to be invalid or unenforceable ; ( ii ) citing prior art against any of the F -star Patents or Platform 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 -examination of any of the F -star Pa tents or Platform Patents ( other than with F - star ’s written agreement ), or becoming a party to or pursuing an interference ; or ( iii ) filing or pursuing any opposition, cancellation, nullity or other like proceedings against any of the F -star Patents or Pla tform Patents ; but excluding any challenge raised as a defense or counterclaim against a claim, action or proceeding asserted by F -star or its Affiliates against Gamma or its Affiliates or Sublicensees