string: The use of bisimilarity in this context is particularly attractive because, as essentially shown in (Hennessy and Milner, 1985), bisimilarity provides an abstraction technique that preserves the truth and falsehood of any formula expressed in the μ-calculus (Kozen, 1983), and hence all CTL∗ (Dam, 1994), CTL (Clarke and Emerson, 1981; McMillan, 1993), and LTL (Pnueli, 1977)