@article{AM2_1973__9_136348,
     author = {JOHN DAVID LOGAN},
     title = {First {Integrals} in the {Discrete} {Variational} {Calculus}},
     journal = {Aequationes mathematicae},
     pages = {210--220},
     publisher = {mathdoc},
     volume = {9},
     year = {1973},
     zbl = {0268.49022},
     url = {http://geodesic.mathdoc.fr/item/AM2_1973__9_136348/}
}