@article{IM_1991__105_3_143905,
     author = {Tomasz Nowicki and Sebastian van Strien},
     title = {Invariant measures exist under a summability condition for unimodal maps.},
     journal = {Inventiones mathematicae},
     pages = {123--136},
     publisher = {mathdoc},
     volume = {105},
     number = {3},
     year = {1991},
     zbl = {0736.58030},
     url = {http://geodesic.mathdoc.fr/item/IM_1991__105_3_143905/}
}