  We present an analytical investigation of exact anticipating synchronization
between two bi-idirectionally coupled time-delayed systems in the case when
these systems are governed by two characteristic times: the delay time in the
coupling and the delay time in the coupled systems. We apply our approach to
interpret the results of recent first experimental observation of anticipating
chaos synchronization in external cavity semiconductor lasers with optical
feedback.We establish that our approach can explain the experimental results
only for special cases.
