; qualified real property interest The terms qualified conservation contribution and qualified real property interest have the respective meanings given such terms by section 170(h), except that paragraph (2)(A) thereof shall be applied without regard to any qualified mineral interest (as defined in paragraph (6) thereof). (c) Special rules (1) Fair market value Fair market value of any National Scenic Trail conservation contribution shall be determined under rules similar to the valuation rules under Treasury Regulations under section 170, except that in any case, to the extent practicable, fair market value shall be determined by reference to the highest and best use of the real property with respect to such contribution. (2) Election irrevocable An election under this section may not be revoked. (3) Denial of double benefit No deduction shall be allowed under this chapter with respect to any qualified conservation contribution with respect to which an election is made under this section. (d) Application with other credits (1) Business credit treated as part of general business credit So much of the credit which would be allowed under subsection (a) for any taxable year (determined without regard to this subsection) that is attributable to property used in a trade or business or held for the production of income shall be treated as a credit listed in section 38(b) for such taxable year (and not allowed under subsection (a)). (2) Personal credit For purposes of this title, the credit allowed under subsection (a) for any taxable year (determined after application of paragraph (1)) shall be treated as a credit allowable under subpart A for such taxable year. (e) Carryforward of unused credit (1) In general If the credit allowable under subsection (a) exceeds the limitation imposed by section 26(a) for any taxable year reduced by the sum of the credit allowable under subpart A (other than this section), such excess shall be carried to the succeeding taxable year and added to the credit allowable under subsection