@article{CMUC_1989__30_1_a16,
     author = {Kraj{\'\i}\v{c}ek, Jan},
     title = {Speed-up for propositional {Frege} systems via generalizations of proofs},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {137--140},
     publisher = {mathdoc},
     volume = {30},
     number = {1},
     year = {1989},
     mrnumber = {995712},
     zbl = {0675.03034},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1989__30_1_a16/}
}