  The formal Heisenberg equations of the Federbush model are linearized and
then are directly integrated applying the method of dynamical mappings. The
fundamental role of two-dimensional free massless pseudo-scalar fields is
revealed for this procedure together with their locality condition taken into
account. Thus the better insight into solvability of this model is obtained
together with the additional phase factor for its general solution, and the
meaning of the Schwinger terms is elucidated.
