Hy. Fan et Y. Fan, <xi vertical bar representation of the inverse of two-particle relative position and its application, COMM TH PHY, 32(2), 1999, pp. 319-320
We derive the [xi\ representation of the inverse of two particles' relative
position which turns out to be an integration operation on the representat
ion and is related to two particles' masses. The representation is useful i
n conveniently solving energy level formula for some dynamic systems.