Simple finite axiomatizations are given for versions of the modal logics K and K4 with non-contingency (or contingency) as the sole modal primitive. This answers two questions of I. L. Humberstone.
"Minimal Non-contingency Logic." Notre Dame J. Formal Logic 36 (2) 230 - 234, Spring 1995. https://doi.org/10.1305/ndjfl/1040248456