ON TOPOLOGICAL-ENTROPY OF TRIANGULAR MAPS OF THE SQUARE

We study the topological entropy of triangular maps of the square. We show that such maps differ from the continuous maps of the interval because there exist triangular maps of the square of ''type 2(infinity)'' with infinite topological entropy. The set of such maps is dense in the space of triangular maps of ''type at most 2(infinity)'' and the topological entropy as a function of the triangular maps of the square is not lower semicontinuous. However, we show that for these maps the characterisation of the lower bounds of the topological entropy depending on the set of periods is the same as for the continuous maps of the interval.