Deduction for estates and trusts accumulating income or distributing corpus

In any taxable year there shall be allowed as a deduction in computing the taxable income of an estate or trust (other than a trust to which subpart B applies), the sum of— The amount determined under subsection (a) shall be treated as consisting of the same proportion of each class of items entering into the computation of distributable net income of the estate or trust as the total of each class bears to the total distributable net income of the estate or trust in the absence of the allocation of different classes of income under the specific terms of the governing instrument. In the application of the preceding sentence, the items of deduction entering into the computation of distributable net income (including the deduction allowed under section 642(c)) shall be allocated among the items of distributable net income in accordance with regulations prescribed by the Secretary. No deduction shall be allowed under subsection (a) in respect of any portion of the amount allowed as a deduction under that subsection (without regard to this subsection) which is treated under subsection (b) as consisting of any item of distributable net income which is not included in the gross income of the estate or trust.