Invariant measures exist under a summability condition for unimodal maps (Q1814172)

Let \(f\) be a universal \(C^ 3\)-function on the interval with negative Schwarzian derivative. If at the critical value \(c\) the iterates \(f^ n=f\circ\ldots\circ f\) of \(f\) have the property that \((f^ n)'(f(c))\) tends to infinity ``fast enough'' then \(f\) admits a unique absolutely continuous (w.r.t. the Lebesgue measure) invariant probability measure. This generalizes a result of Collet and Eckmann.