The purpose of this article is to introduce Monadic Second-order Logic as a practical means of specifying regularity. The logic is a highly succinct alternative to the use of regular expressions. We have built a tool MONA, which acts as a decision procedure and as a translator to finite-state automata. The tool is based on new algorithms for minimizing finitestate automata that use binary decision diagrams (BDDs) to represent transition functions in compressed form. A byproduct of this work is a new bottom-up algorithm to reduce BDDs in linear time without hashing. The potential

) Henrik Reif Andersen Department of Computer Science Technical University of Denmark Building 344, DK-2800 Lyngby, Denmark. Abstract A major obstacle in applying finite-state model checking to the verification of large systems is the combinatorial explosion of the state space arising when many loosely coupled parallel processes are considered. The problem also known as the state-explosion problem has been attacked from various sides. This paper presents a new approach based on partial model checking: Parts of the concurrent system are gradually removed while transforming the specification accordingly. When the intermediate specifications constructed in this manner can be kept small, the stateexplosion problem is avoided. Experimental results with a prototype implemented in Standard ML, shows that for Milner's Scheduler --- an often used benchmark --- this approach improves on the published results on Binary Decision Diagrams and is comparable to results obtained using generalized...

Much work in automatic verification considers families of similar finite-state systems. But an often overlooked property is that sometimes a single finite-state system can be used to describe a parameterized, infinite family of systems. Thus verification of unbounded state spaces can take place by reduction to finite ones.

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