@article{10_4064_cm_22_1_135_151,
     author = {J. Kisy\'nski},
     title = {On second order hyperbolic equation with two independent variables},
     journal = {Colloquium Mathematicum},
     pages = {135--151},
     publisher = {mathdoc},
     volume = {22},
     number = {1},
     year = {1970},
     doi = {10.4064/cm-22-1-135-151},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-22-1-135-151/}
}