On the ambiguity of determination of interfering resonances parameters

The general form of solutions for parameters of interfering Breit-Wigner resonances is found. The number of solutions is determined by the properties of roots of corresponding characteristic equation and does not exceed $2^{N-1}$, where $N$ is the number of resonances. For resonances of more complicated form, provided that their amplitudes satisfy certain conditions, for any $N\ge2$ multiple solutions also exist.