; (D) in paragraph (13), by striking the period at the end and inserting ; and ; and (E) by adding at the end the following: (14) setting forth the standards for demonstrating exceptional circumstances under sections 303(e)(1) and 315(e)(2). ; (2) by amending subsection (e) to read as follows: (e) Evidentiary standards (1) Presumption of validity The presumption of validity under section 282(a) shall apply to previously issued claims of a patent that is challenged in an inter partes review under this chapter. (2) Burden of proof In an inter partes review under this chapter— (A) the petitioner shall have the burden of proving a proposition of unpatentability of a previously issued claim of a patent by clear and convincing evidence; and (B) the petitioner shall have the burden of persuasion, by a preponderance of the evidence, with respect to a proposition of unpatentability for any substitute claim proposed by the patent owner. ; and (3) by adding at the end the following: (f) Claim construction For the purposes of this chapter— (1) each challenged claim of a patent, and each substitute claim proposed in a motion to amend, shall be construed as the claim would be construed under section 282(b) in an action to invalidate a patent, including by construing each such claim in accordance with— (A) the ordinary and customary meaning of the claim as understood by a person having ordinary skill in the art to which the claimed invention pertains; and (B) the prosecution history pertaining to the patent