On homoclinic tangencies, hyperbolicity, creation of homoclinic orbits andvariation of entropy

We show that an assertion made in Gambaudo el al(1999 Nonlinearity 12 443) is not correct and, as a consequence, we confirm and even generalize previo us results by those authors (Gambaudo and Rocha 1994 Nonlinearity 7 1251-9) . Another main result states that variation of the topological entropy of s urface diffeomorphisms is always associated with the unfolding of homoclini c tangencies.