M. J. Cresswell. Alternative completeness theorems for modal systems. Notre Dame Journal of Formal Logic, 8(4):339-345, 1967. [doi]
@article{Cresswell67a,
title = {Alternative completeness theorems for modal systems},
author = {M. J. Cresswell},
year = {1967},
doi = {10.1305/ndjfl/1094068851},
url = {http://dx.doi.org/10.1305/ndjfl/1094068851},
researchr = {https://researchr.org/publication/Cresswell67a},
cites = {0},
citedby = {0},
journal = {Notre Dame Journal of Formal Logic},
volume = {8},
number = {4},
pages = {339-345},
}