@article{JRAM_1988__385_153014,
     author = {Chaohao Gu},
     title = {A class of boundary problems for extremal surfaces of mixed type in {Minkowski} 3-space.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {195--202},
     publisher = {mathdoc},
     volume = {385},
     year = {1988},
     zbl = {0635.49019},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1988__385_153014/}
}