P. J. Fitzpatrick. An extension of Venn diagrams. Notre Dame Journal of Formal Logic, 14(1):77-86, 1973. [doi]
@article{Fitzpatrick73,
title = {An extension of Venn diagrams},
author = {P. J. Fitzpatrick},
year = {1973},
doi = {10.1305/ndjfl/1093890810},
url = {http://dx.doi.org/10.1305/ndjfl/1093890810},
researchr = {https://researchr.org/publication/Fitzpatrick73},
cites = {0},
citedby = {0},
journal = {Notre Dame Journal of Formal Logic},
volume = {14},
number = {1},
pages = {77-86},
}