Closed invariant curves of a noncontinuously dififerentiable recurrence

Abstract

The determination of invariant curves (when they exist) is a key problem in the study of the phase portrait of a second order autonomous recurrence (cf. [1])

$${x_{n + 1}} = g\left( {{x_{n,}}{y_n}} \right)\quad {y_{n + 1}} = f\left( {{x_n},{y_n}} \right)$$

((1))

.