| Twins in Logic - Identical and Otherwise
Lloyd Humberstone
Connectives are twins in a logic, according to a metaphor of Łukasiewicz, when they behave ‘in the same way’ according to that logic. There are, however, looser and stricter ways of understanding that phrase, informally contrasted in §1 and then precisely defined and illustrated in §3, after a glance at related work by Michael Byrd and Evgeni Zolin in §2. §4 returns to the motivating case of the Ł-modal system, with its ‘twin possibility operators.’ One rather detailed discussion arising from §3 is deferred to an Appendix, so as not to interrupt the flow.
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