by Antonín Kučera, Javier Esparza, This is a full and revised version of a paper which previously appeared in Proceedings of CSL`99. January 2000, 26 pages.
FIMU-RS-2000-01. Available as Postscript, PDF.
We study the following problem: Given a transition system T and its quotient T/~ under an equivalence ~, which are the sets L, L` of Hennessy-Milner formulae such that: if f belongs to L and T satisfies f, then T/~ satisfies f; if f belongs to L` and T/~ satisfies f, then T satisfies f.