@article{CM_1937__4__112_0,
     author = {Freudenthal, Hans},
     title = {Zur intuitionistischen Deutung logischer Formeln},
     journal = {Compositio Mathematica},
     publisher = {Johnson Reprint Corporation},
     volume = {4},
     year = {1937},
     pages = {112-116},
     zbl = {0015.24201},
     language = {de},
     url = {http://www.numdam.org/item/CM_1937__4__112_0}
}

Freudenthal, Hans. Zur intuitionistischen Deutung logischer Formeln. Compositio Mathematica, Volume 4 (1937) , pp. 112-116. http://www.numdam.org/item/CM_1937__4__112_0/