5 U.S.C. § 8431. Certain transfers to be treated as a separation

1. (a)
   (a)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.
2. (b)
   (b)

   The retirement systems described in this subsection are—

   1. (1)
      (b)(1)the retirement system under this chapter;
   2. (2)
      (b)(2)the retirement system under subchapter III of chapter 83; and
   3. (3)
      (b)(3)any other retirement system under which individuals may contribute to the Thrift Savings Fund through withholdings from pay.