  We give a combinatorial proof of a theorem first proved by Souto which says
the following. Let M_1 and M_2 be simple 3-manifolds with connected boundary of
genus g>0. If M_1 and M_2 are glued via a complicated map, then every minimal
Heegaard splitting of the resulting closed 3-manifold is an amalgamation. This
proof also provides an algorithm to find a bound on the complexity of the
gluing map.
