A few remarks on intermediate subalgebras of an inclusion of C*-algebras (2311.07244v3)

Abstract: We show that the angle between intermediate $C^*$-subalgebras of an inclusion of simple $C^*$-algebras with finite Watatani index is stable. The notion of angle is instrumental in providing a bound for the cardinality of the lattice of intermediate subalgebras for an irreducible inclusion of simple $C^*$-algebras. We improve the existing upper bound for the cardinality of this set.