Section 818(f) provides that the same item may not be deducted more than once under subpart B, part I, subchapter L, chapter 1 of the Code (relating to the determination of taxable investment income), and more than once under subpart C, part I, subchapter L, chapter 1 of the Code (relating to the determination of gain or loss from operations). [T.D. 6558, 26 FR 2790, Apr. 4, 1961]