  A detailed consideration is given to the translation-invariant theory of
Tulub polaron constructed without the use of Pekar ansatz. A fundamental result
of the theory is that the value of the polaron energy is lower than that
obtained on the basis of Pekar ansatz which was considered as an asymptotically
exact solution in the strong coupling limit. In the case of bipolarons the
theory yields the best values of the coupling energy and critical parameters of
their stability. Numerous physical consequences of the existence of
translation-invariant polarons and bipolarons are discussed.
