Assuming that at least 50 percent of the value of the total assets of the corporation satisfies the requirements specified in this subparagraph, and that the limiting provisions of subparagraph (B) of section 851(b)(4) and subparagraph (2) of this paragraph are not violated, the corporation will satisfy the requirements of section 851(b)(4), notwithstanding that the remaining assets do not satisfy the diversification requirements of subparagraph (A) of section 851(b)(4). For example, a corporation may own all the stock of another corporation, provided it otherwise meets the requirements of subparagraphs (A) and (B) of section 851(b)(4).
26 C.F.R. §1.851-2