Czeslaw Lejewski. A single axiom for the mereological notion of proper part. Notre Dame Journal of Formal Logic, 8(4):279-285, 1967. [doi]
@article{Lejewski67,
title = {A single axiom for the mereological notion of proper part},
author = {Czeslaw Lejewski},
year = {1967},
doi = {10.1305/ndjfl/1094068839},
url = {http://dx.doi.org/10.1305/ndjfl/1094068839},
researchr = {https://researchr.org/publication/Lejewski67},
cites = {0},
citedby = {0},
journal = {Notre Dame Journal of Formal Logic},
volume = {8},
number = {4},
pages = {279-285},
}