26 USC 2519 - Dispositions of certain life estates

(a) General rule 
For purposes of this chapter and chapter 11, any disposition of all or part of a qualifying income interest for life in any property to which this section applies shall be treated as a transfer of all interests in such property other than the qualifying income interest.
(b) Property to which this subsection applies 
This section applies to any property if a deduction was allowed with respect to the transfer of such property to the donor
(1) under section 2056 by reason of subsection (b)(7) thereof, or
(2) under section 2523 by reason of subsection (f) thereof.
(c) Cross reference 
For right of recovery for gift tax in the case of property treated as transferred under this section, see section 2207A (b).