@article{MV_1965_17_2_a9,
     author = {S. Lajos},
     title = {On existence of the identity element in a semigroup},
     journal = {Matemati\v{c}ki vesnik},
     pages = {155 },
     year = {1965},
     volume = {17},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/MV_1965_17_2_a9/}
}