The amount of income for the taxable year required to be distributed currently to such beneficiary, whether distributed or not. If the amount of income required to be distributed currently to all beneficiaries exceeds the distributable net income (computed without the deduction allowed by section
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(c), relating to deduction for charitable, etc., purposes) of the estate or trust, then, in lieu of the amount provided in the preceding sentence, there shall be included in the gross income of the beneficiary an amount which bears the same ratio to distributable net income (as so computed) as the amount of income required to be distributed currently to such beneficiary bears to the amount required to be distributed currently to all beneficiaries. For purposes of this section, the phrase “the amount of income for the taxable year required to be distributed currently” includes any amount required to be paid out of income or corpus to the extent such amount is paid out of income for such taxable year.