  The recent multiple-solution problem in extracting physics information from a
fit to the experimental data in high energy physics is reviewed in a
mathematical viewpoint. All these multiple solutions were found via a fit
process previously, while in this letter we prove that if the sum of two
coherent Breit-Wigner functions is used to fit the measured distribution, there
should be two and only two non-trivial solutions, and they are related to each
other by analytical formulae. For real experimental measurements in more
complicated situations, we also provide a numerical method to derive the other
solution from the already obtained one. The excellent consistency between the
exact solution obtained this way and the fit process justifies the method. From
our results it is clear that the physics interpretation should be very
different depending on which solution is selected. So we suggest that all the
experimental measurements with potential multiple solutions be re-analyzed to
find the other solution because the result is not complete if only one solution
is reported.
