@article{10_4064_ap_67_2_111_120,
     author = {Jerzy Kalina and Antoni Pierzchalski and Pawe{\l} Walczak},
     title = {Only one of generalized gradients can be elliptic},
     journal = {Annales Polonici Mathematici},
     pages = {111--120},
     publisher = {mathdoc},
     volume = {67},
     number = {2},
     year = {1997},
     doi = {10.4064/ap-67-2-111-120},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-67-2-111-120/}
}