“…Sahlqvist theory is currently a very active field of research. This field has significantly broadened its scope in recent years, extending the state of the art and the benefits of Sahlqvist theory from modal logic to a class of logics which includes, among others, intuitionistic and lattice-based (modal) logics [32,20], substructural logics [44,59,21], non-normal modal logics [28,51], hybrid logics [24], many-valued logics [45], mu-calculus [71,10,8,2,9], and coalgebraic logic [46,57]. The common ground to these results is the recognition that algebraic and order-theoretic notions play a fundamental role in the various incarnations of the Sahlqvist phenomenon.…”