@article{IM_1991__105_3_143926,
     author = {Yujiro Kawamata},
     title = {On the length of a extremal rational curve.},
     journal = {Inventiones mathematicae},
     pages = {609--612},
     publisher = {mathdoc},
     volume = {105},
     number = {3},
     year = {1991},
     zbl = {0751.14007},
     url = {http://geodesic.mathdoc.fr/item/IM_1991__105_3_143926/}
}