@article{10_4064_cm_56_1_147_151,
     author = {Ryszard Grz\k{a}\'slewicz},
     title = {Extreme symmetric norms on $R^2$},
     journal = {Colloquium Mathematicum},
     pages = {147--151},
     publisher = {mathdoc},
     volume = {56},
     number = {1},
     year = {1988},
     doi = {10.4064/cm-56-1-147-151},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-56-1-147-151/}
}