Abstract.
It is proved that in the variety of positive Sugihara monoids, every finite subdirectly irreducible algebra is a retract of a free algebra. It follows that every quasivariety of positive Sugihara monoids is a variety, in contrast with the situation in several neighboring varieties. This result shows that when the logic R-mingle is formulated with the Ackermann constant t, then its full negation-free fragment is hereditarily structurally complete.
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Received August 28, 2005; accepted in final form July 31, 2006.
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Olson, J.S., Raftery, J.G. Positive Sugihara monoids. Algebra univers. 57, 75–99 (2007). https://doi.org/10.1007/s00012-007-2022-4
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DOI: https://doi.org/10.1007/s00012-007-2022-4