Accelerated portion of credit
For purposes of paragraph (2), the accelerated portion of the credit for the prior taxable years with respect to any amount of basis is the excess of—
(A) the aggregate credit allowed by reason of this section (without regard to this subsection) for such years with respect to such basis, over
(B) the aggregate credit which would be allowable by reason of this section for such years with respect to such basis if the aggregate credit which would (but for this subsection) have been allowable for the entire compliance period were allowable ratably over 15 years.