Explicit formulae are given for the saddle connection of an integrable family
of standard maps studied by Y. Suris. When the map is perturbed this connection
is destroyed, and we use a discrete version of Melnikov's method to give an
explicit formula for the first order approximation of the area of the lobes of
the resultant turnstile. These results are compared with computations of the
lobe area.Comment: laTex file with 6 eps figure