The classical Hennessy-Milner theorem says that two states of an image-finite transition system are bisimilar if and only if they satisfy the same formulas in a certain modal logic. In this paper we study this type of result in a general context, moving from transition systems to coalgebras and from bisimilarity to coinductive predicates. We formulate when a logic fully characterises a coinductive predicate on coalgebras, by providing suitable notions of adequacy and expressivity, and give sufficient conditions on the semantics. The approach is illustrated with logics characterising similarity, divergence and a behavioural metric on automata.

@article{paperbot1256,
  title = {Expressive Logics for Coinductive Predicates},
  author = {Clemens Kupke and Jurriaan Rot},
  journal = {Logical Methods in Computer Science},
  volume = {Volume 17, Issue 4},
  year = {2021},
  doi = {10.46298/lmcs-17(4:19)2021}
}