@article{AUCMP_2009_50_1_a3,
     author = {Kala, V. and Kepka, Tom\'a\v{s} and Phillips, J. D.},
     title = {Various subsemirings of the field $\Bbb Q$ of rational numbers},
     journal = {Acta Universitatis Carolinae. Mathematica et Physica},
     pages = {29--59},
     year = {2009},
     volume = {50},
     number = {1},
     mrnumber = {2569468},
     zbl = {1192.16044},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AUCMP_2009_50_1_a3/}
}