The Relevant Equivalence Property
Lloyd Humberstone, R. K. Meyer · Logic Journal of IGPL · 2007
The pure implicational and the multiplicative fragments of a range of propositional relevant (and other) logics are shown to have the property that any two formulas equivalent in such a logic are constructed from exactly the same propositional variables – as opposed to merely having (as the definition of relevance itself would require) some propositional variable in common.