((a)) ** General rule** No deduction shall be allowed to the issuing corporation for any premium paid or incurred upon the repurchase of a bond, debenture, note, or certificate or other evidence of indebtedness which is convertible into the stock of the issuing corporation, or a corporation in the same parent-subsidiary controlled group (within the meaning of section 1563(a)(1)) as the issuing corporation, to the extent the repurchase price exceeds an amount equal to the adjusted issue price plus a normal call premium on bonds or other evidences of indebtedness which are not convertible. The preceding sentence shall not apply to the extent that the corporation can demonstrate to the satisfaction of the Secretary that such excess is attributable to the cost of borrowing and is not attributable to the conversion feature.

((b)) ** Adjusted issue price** For purposes of subsection (a), the adjusted issue price is the issue price (as defined in sections 1273(b) and 1274) increased by any amount of discount deducted before repurchase, or decreased by any amount of premium included in gross income before repurchase by the issuing corporation.