  The inversion-asymmetry of the emission source in relativistic heavy ion
collision under the Bertsch-Pratt convention is discussed and explicitly
exhibited by a Monte Carlo model. The Gaussian source function popularly used
in the HBT analysis of relativistic heavy ion collisions is invalid in this
case. An inversion-asymmetric source function is suggested. A method for
extracting the inversion-asymmetry degree of the source together with the
source size from experimental data is proposed.
