Abstract. We study languages over infinite alphabets equipped with some structure that can be tested by recognizing automata. We develop a framework for studying such alphabets and the ensuing automata theory, where the key role is played by an automorphism group of the alphabet. In the process, we generalize nominal sets due to Gabbay and Pitts.

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A syntactic framework called SGSOS, for defining well-behaved Markovian stochastic transition systems, is introduced by analogy to the GSOS congruence format for nondeterministic processes. Stochastic bisimilarity is guaranteed a congruence for systems defined by SGSOS rules. Associativity of parallel composition in stochastic process algebras is also studied within the framework.

Polyadic coalgebraic modal logic is studied in the setting of locally presentable categories. It is shown that under certain assumptions, accessible functors admit expressive logics for their coalgebras. Examples include typical functors used to describe systems with name binding, interpreted in nominal sets.

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Abstract. Weighted transition systems are defined, parametrized by a commutative monoid of weights. These systems are further understood as coalgebras for functors of a specific form. A general rule format for the SOS specification of weighted systems is obtained via the coalgebraic approach of Turi and Plotkin. Previously known formats for labelled transition systems (GSOS) and stochastic systems (SGSOS) appear as special cases.