  Melting of a bicrystal along the grain boundary is discussed. A triple
junction plays a crucial role in the velocity selection problem in this case.
In some range of the parameters an entirely analytical solution of this problem
is given. This allows to present a transparent picture of the structure of the
selection theory. We also discuss the selection problem in the case of the
growth of a ``eutectoid dendrite'' where a triple junction is present because
three phases are involved in the eutectoid reaction.
