  A geometric approach to the equation found by Hietarinta and Viallet, which
satisfies the singularity confinement criterion but exhibits chaotic behavior,
is presented. It is shown that this equation can be lifted to an automorphism
of a certain rational surface and can therefore be considered to be the action
of an extended Weyl group of indefinite type. A method to calculate its
algebraic entropy by using the theory of intersection numbers is presented.
