  The problem of the diagonalization of the flavor-neutrino propagator mat rix
is investigated in the theory with flavor-mixing mass terms in Lagrangian. For
this purpose we examine one-pole structures of flavor-neutrino propa gators,
leading to physical neutrino masses, and discuss the relation of the pro
pagator diagonalizaion to the diagonalizaion of the mass matrix in Lagrangian.
In connection with the paper by Blasone et al., it is pointed out that t here
is no compelling reason for fixing the mass parameters, althought this fixi ng
is necessary in order to construct the flavor Hilbert space.
