@article{CM_1968__20__1_0,
     author = {Van Dalen, D. and Dijkman, J. G. and Kleene, S. C. and Troelstra, A. S.},
     title = {Preface},
     journal = {Compositio Mathematica},
     pages = {1--1},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {20},
     year = {1968},
     language = {en},
     url = {http://www.numdam.org/item/CM_1968__20__1_0/}
}