  Delayed feedback laser dynamics is described by means of Lang-Kobayashi
equation model. Since a lot of initial states asymptotically approach to
periodic attractor in the phase space, only periodic steady-state regimes have
been studied here. Lyapunov transformation allows us to reduce problem to the
differential equation of the first order whereas the spectrum of laser
oscillation is governed by the appropriate eigen value problem. Using the
symmetry proves that there is the dual laser system with anticipated feedback
which has the same dynamic characteristics as laser with delayed feedback.
