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_posts/2017-11-15- bernardi.md

+---
+title: Visitor to the group, Giovanni Bernardi, IRIF, Paris
+---
+
+[Dr Giovanni Bernardi](https://www.researchgate.net/profile/Giovanni_Bernardi2) of Paris Diderot University / [IRIF]( https://www.irif.fr//en/index) 
+visited the group in November to give a talk on his current work on must- testing for message passing concurrency. 
+
+[Giovanni](https://www.irif.fr/~gio/index.xhtml) is a long standing co-author with Andrea Cerone and has worked on Formal methods 
+and the Semantics of programming languages, focusing on concurrency, types (overall behavioural ones [BETTY]), and models of types. 
+The title of his talk was Full-abstraction for Must Testing Preorders. 
+
+Abstract: The client must preorder relates tests (clients) instead of processes (servers). 
+The existing characterisation of this preorder is unsatisfactory for it relies 
+on the notion of usable clients which, in turn, are defined using an existential 
+quantification over the servers that ensure client satisfaction. In this talk, 
+we characterise the set of usable clients for finite-branching LTSs, and give a 
+sound and complete decision procedure for it. We also provide a novel coinductive 
+characterisation of the client preorder, which we use to argue that the preorder 
+is decidable, thus positively answering the question remained open in the literature.