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    | • | A
    formal description technique standardized in 
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    |  | 1988 by International Telecommunication Union 
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    | • | Intended
    for description of communication 
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    |  | protocols 
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    | • | Used
    on a variety of distributed, concurrent, 
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    |  | communicating,
    asynchronous systems 
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    | • | Many support tools exists, but no framework for 
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    |  | theorem-proving
    based verification 
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    | • | Main
    building blocks are processes represented 
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    |  | by extended finite-state machines and delaying 
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    |  | and
    instantaneous communication links 
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