@article{CM_1968__20__83_0,
     author = {Grzegorczyk, Andrzej},
     title = {Assertions depending on time and corresponding logical calculi},
     journal = {Compositio Mathematica},
     pages = {83--87},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {20},
     year = {1968},
     mrnumber = {230599},
     zbl = {0175.26302},
     language = {en},
     url = {http://www.numdam.org/item/CM_1968__20__83_0/}
}