Hy. Fan et Nl. Liu, Differential forms of completeness relation in two-mode <xi vertical bar-<eta vertical bar representations, COMM TH PHY, 32(4), 1999, pp. 611-614
On the basis of the common eigenvectors <eta \ and <xi \, which respectivel
y are eigenvectors of two particles' relative position and total momentum a
s well as center-of-mass coordinate and relative momentum, we find that the
re exist differential forms of completeness relation. The applications of t
he new completeness relation are pointed out. Throughout our discussion the
technique of differentiation within an ordered product of operators is ful
ly employed.