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Principal congruences in De Morgan algebras. (English) Zbl 0595.06013
It is shown that, for a Kleene algebra, the intersection of two principal congruences is always a principal congruence. However, an example is given to show that this need not be the case for a de Morgan algebra (of which Kleene algebras are a particular example). This answers a question of H. P. Sankappanavar (and T. S. Blyth and J. C. Varlet).

06D30 De Morgan algebras, Łukasiewicz algebras (lattice-theoretic aspects)
06B10 Lattice ideals, congruence relations
03G25 Other algebras related to logic
Full Text: DOI
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