required taxable year
For purposes of this section, the term “required taxable year” means the taxable year determined under section 706(b), 1378, or 441(i) without taking into account any taxable year which is allowable by reason of business purposes. Solely for purposes of the preceding sentence, sections 706(b), 1378, and 441(i) shall be treated as in effect for taxable years beginning before January 1, 1987 .