definiens: means any additional payment to Ironwood undereither Section 4.6.2(a ) or 4.6.2(b ) ( or portion thereof ) attributable to a Tax that reduces the U.S. federalincome tax liability of Ironwood as a result of a foreign tax credit actually claimed by Ironwood . Forpurposes of the preceding sentence, to the extent any additional payment ( or portion thereof ) to Ironwoodunder Section 4.6.2(b ) ( but, for avoidance of doubt, not Section 4.6.2(a ) ) has not been classified as a TaxBenefit Amount within the Applicable Period ( as defined in Section 4.6.4 below ), then such additionalpayment ( or portion thereof ) will be deemed to be a Tax Benefit Amount and will be deducted from theamount of royalties owed to Ironwood in accordance with Section 4.3.4 following the close of suchApplicable Period