Closure operators 6 Approximate reasoning 4 Approximation theory 4 Bounded distributive lattices 4 Closure systems and fuzzy consequence relations 4 Computer science 4 Fuzzy closure operators 4 Fuzzy sets 4 Implication measures 4 Mathematical operators 4 Priestley spaces 4 AMS subject classification (1991): 06D05 2 Congruence relations 2 Join-homomorphisms 2 Lattice homomorphisms 2 Priestley relations 2 Quantifiers 2 Varieties 2 closure operators 2 filters 2 ideals 2 lattice homomorphisms 2 quantifiers 2 sublattices 2