For purposes of this subchapter, separation from Government employment includes a transfer from a position that is subject to one of the retirement systems described in subsection (b) to a position that is not subject to any of them.
The retirement systems described in this subsection are—
(1) the retirement system under this chapter;
(2) the retirement system under subchapter III of chapter 83; and
(3) any other retirement system under which individuals may contribute to the Thrift Savings Fund through withholdings from pay.
(Added Pub. L. 106–168, title II, § 203(a)(1), Dec. 12, 1999, 113 Stat. 1820.)