26 U.S.C. § 676 — Power to revoke

(a) General rule The grantor shall be treated as the owner of any portion of a trust, whether or not he is treated as such owner under any other provision of this part, where at any time the power to revest in the grantor title to such portion is exercisable by the grantor or a non-adverse party, or both. (b) Power affecting beneficial enjoyment only after occurrence of event Subsection (a) shall not apply to a power the exercise of which can only affect the beneficial enjoyment of the income for a period commencing after the occurrence of an event such that a grantor would not be treated as the owner under section 673 if the power were a reversionary interest. But the grantor may be treated as the owner after the occurrence of such event unless the power is relinquished.