definiens: means any challenge in a lega l or administrative proceeding to the patentability, validity, ownership or enforceability of any of the Silence Background Patents, Silence Research Patents or Joint Research Patents ( or any claim the reof ), including by : ( x ) filing or pursuing a declarato ry judgment action in which any of the Silence Back ground Patents, Silence Research Patents or Joint Research Patents is alleged to be invalid or unenforceable ; ( y ) citing prior art against any of the Silence Background Patents, Silence Research Patent s or Joint Research Patents ( other than art required to be cited by Applicable Law, - 107 / 130 - CONFIDENTIAL including under a duty of candor to a patent office ), filing a request for or pursuing a re- examination of any of the Silence Background Patents, Silence Rese arch Patents or Joint Research Patents ( other than with Silence ’s written agreement ), or becoming a pa rty to or pursuing an interference ; or ( z ) filing or pursuing any opposition, cancellation, nullity, or other like proceedings against any of the Silence Background Patents, Silence Research Patents or Joi nt Research Patents ; but excluding ( i ) any chal lenge raised by AZ or its Affiliates as a defense a gainst a claim, action, or proceeding asserted by Silence or its Affiliates against AZ or its Affilia tes or Sublicensees ; ( ii ) any existing challenges, whether in a court or administrative proceeding, agai nst a Silence Background Patent, raised by a Third Party that is acquired by AZ or its Affiliates after the Effective Date, provided that AZ, and AZ procures that its Affiliates, promptly withdraws from any such ex isting challenge ; and ( iii ) any legal or a dministrative proceeding derived from a bona fide inventorship dispute between AZ or its Affiliates a nd Silence or its Affiliates for any AZ Research Patent, Joint Re search Patent or Silence Research Patent