Survivorship.
Survivorship. If the order of deaths of the decedent and his spouse cannot be established by proof, a presumption (whether supplied by local law, the decedent's will, or otherwise) that the decedent was survived by his spouse will be recognized as satisfying paragraph (b)(1) of 20.2056(a)1, but only to the extent that it has the effect of giving to the spouse an interest in property includible in her gross estate under Part III of Subchapter A of Chapter 11. Under these circumstances, if an estate tax return is required to be filed for the estate of the decedent's spouse, the marital deduction will not be allowed in the final audit of the estate tax return of the decedent's estate with respect to any property interest which has not been finally determined to be includible in the gross estate of his spouse.