@article{10_4064_fm_80_1_5_12,
     author = {L. Szczerba},
     title = {The notion of an elementary subsystem for a {Boolean-valued} relational system},
     journal = {Fundamenta Mathematicae},
     pages = {5--12},
     publisher = {mathdoc},
     volume = {80},
     number = {1},
     year = {1973},
     doi = {10.4064/fm-80-1-5-12},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-80-1-5-12/}
}