@article{AULFM_1992_05_a12,
     author = {Jasku{\l}a, Janusz and Lech, Jaros{\l}aw},
     title = {On the sets {A} + {A} and {A} - {A}},
     journal = {Acta Universitatis Lodziensis. Folia Mathematica},
     publisher = {mathdoc},
     volume = {05},
     year = {1992},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AULFM_1992_05_a12/}
}