@article{PIM_1987_N_S_42_56_a2,
     author = {Ivan Gutman and Jerzy Cioslowski},
     title = {Bounds for the {Number} of {Perfect} {Matchings} in {Hexagonal} {Systems}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {21 },
     year = {1987},
     volume = {_N_S_42},
     number = {56},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PIM_1987_N_S_42_56_a2/}
}