@article{10_4064_ap_4_1_30_39,
     author = {A. Krzywicki and J. Rzewuski and J. Zamorski and A. Zi\k{e}ba},
     title = {Non-local problems in the calculus of variations {(II)}},
     journal = {Annales Polonici Mathematici},
     pages = {30--39},
     publisher = {mathdoc},
     volume = {4},
     number = {1},
     year = {1957},
     doi = {10.4064/ap-4-1-30-39},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-4-1-30-39/}
}