A gift made by one spouse to any person other than his spouse shall, for the purposes of this chapter, be considered as made one-half by him and one-half by his spouse, but only if at the time of the gift each spouse is a citizen or resident of the United States. This paragraph shall not apply with respect to a gift by a spouse of an interest in property if he creates in his spouse a general power of appointment, as defined in section
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(c), over such interest. For purposes of this section, an individual shall be considered as the spouse of another individual only if he is married to such individual at the time of the gift and does not remarry during the remainder of the calendar year.