@article{PM_1988_1988_1_a3,
     author = {Musielak, Ryszard and Popenda, Jerzy},
     title = {Las soluciones peri\'odicas de la ecuaci\'on en diferencias no lineal de segundo orden.},
     journal = {Publicacions matem\`atiques},
     pages = {49-56},
     publisher = {mathdoc},
     volume = {32},
     number = {1},
     year = {1988},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PM_1988_1988_1_a3/}
}