Nuel D. Belnap Jr., Hugues Leblanc, Richmond H. Thomason. On not strengthening intuitionistic logic. Notre Dame Journal of Formal Logic, 4(4):313-320, 1963. [doi]
@article{BelnapLT63,
title = {On not strengthening intuitionistic logic},
author = {Nuel D. Belnap Jr. and Hugues Leblanc and Richmond H. Thomason},
year = {1963},
doi = {10.1305/ndjfl/1093957658},
url = {http://dx.doi.org/10.1305/ndjfl/1093957658},
researchr = {https://researchr.org/publication/BelnapLT63},
cites = {0},
citedby = {0},
journal = {Notre Dame Journal of Formal Logic},
volume = {4},
number = {4},
pages = {313-320},
}