26 CFR §1.1312-4 — -4 Double disallowance of a deduction or credit.

1. (a)Paragraph (4) of section 1312 applies if the determination disallows a deduction or credit which should have been, but was not, allowed to the same taxpayer for another taxable year or to a related taxpayer for the same or another taxable year. This is one of the two circumstances in which the maintenance of an inconsistent position is not a requirement for an adjustment but the requirements in paragraph (b) of § 1.1311(b)-2 must be fulfilled (correction not barred at time of erroneous action).
2. (b)The application of paragraph (a) of this section may be illustrated by the following examples: