@article{10_4064_ap_8_1_5_12,
     author = {Stanis{\l}aw Go{\l}\k{a}b and M. Kucharzewski},
     title = {On the notion of gradient. {II.} {A} certain extremal property of direction of the gradient vector},
     journal = {Annales Polonici Mathematici},
     pages = {5--12},
     publisher = {mathdoc},
     volume = {8},
     number = {1},
     year = {1960},
     doi = {10.4064/ap-8-1-5-12},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-8-1-5-12/}
}