To request cancellation of one or more claims of a patent in an inter partes review (IPR), a petitioner must challenge the claim on the basis that the claim is unpatentable under 35 U.S.C §102 or 103, in view of prior art patents or printed publications. 35 U.S.C. § 311(b).  Two ways a patent owner can disqualify references relied upon by the petitioner for unpatentability are by (i) asserting that the petitioner did not set forth sufficient evidence showing that the reference qualifies as a printed publication, or (ii) antedating the reference to show that the date of invention is prior to the critical date of the reference.