@article{AMLG_1987__26_138050,
     author = {Petr H\'ajek and Jeff Paris},
     title = {Combinatorial principles concerning approximations of functions.},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {13--28},
     publisher = {mathdoc},
     volume = {26},
     year = {1987},
     zbl = {0645.03057},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1987__26_138050/}
}