@article{CMUC_1975_16_2_a15,
     author = {Pudl\'ak, Pavel},
     title = {The observational predicate calculus and complexity of computations {(Preliminary} communication)},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {395--398},
     year = {1975},
     volume = {16},
     number = {2},
     mrnumber = {0386346},
     zbl = {0311.02021},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1975_16_2_a15/}
}