  The wall crossing formula of Kontsevich and Soibelman gives an implicit
relation between the BPS indices on two sides of the wall of marginal stability
by equating two symplectomorphisms constructed from the indices on two sides of
the wall. The wall crossing formulae of Manschot, Pioline and the author give
two apparently different explicit expressions for the BPS index on one side of
the wall in terms of the BPS indices on the other side. We prove the
equivalence of all the three formulae.
