Abstract: Iterations of continuous self maps on the interval are the most simple model, which arise some interesting mathmatics structures, in dynamical systems. These systems depend on a characteristic parameter controlled with experiment. The paper discusses the contents of unimodal dynamical systems, proving the uniqueness of λP and then one between 0 and 0.382 9 as unimodal differentiable flat-top functions for any MSS sequence P. It draws a conlusion from the uniqueness of P>RL, and therefore one of P>RL2 in special circumstances for trapezoid functions.