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     1.5 +<HTML><HEAD><TITLE>HOL/UNITY/README</TITLE></HEAD><BODY>
     1.6 +
     1.7 +<H2>UNITY--Chandy and Misra's UNITY formalism</H2>
     1.8 +
     1.9 +<P>The book <EM>Parallel Program Design: A Foundation</EM> by Chandy and Misra
    1.10 +(Addison-Wesley, 1988) presents UNITY, which consists of an abstract
    1.11 +programming language of guarded assignments and an associated calculus.
    1.12 +Misra's 1994 paper "A Logic for Concurrent Programming" presents "New UNITY",
    1.13 +giving more elegant foundations for a more general class of languages.
    1.14 +
    1.15 +<P> This directory is a preliminary formalization of New UNITY.  The Isabelle
    1.16 +examples may not represent the most natural treatment of UNITY style.  Hand
    1.17 +UNITY proofs tend to be written in the forwards direction, as in informal
    1.18 +mathematics, while Isabelle works best in a backwards (goal-directed) style.
    1.19 +
    1.20 +<P>
    1.21 +The syntax, also, is rather unnatural.   Programs are expressed as sets of 
    1.22 +commands, where each command is a relation on states.  Quantification over 
    1.23 +commands using [] is easily expressed.  At present, there are no examples of
    1.24 +quantification using ||.
    1.25 +
    1.26 +<P>
    1.27 +The directory presents a few small examples, mostly taken from Misra's 1994
    1.28 +paper:
    1.29 +<UL>
    1.30 +<LI>common meeting time
    1.31 +
    1.32 +<LI>the token ring
    1.33 +
    1.34 +<LI>the communication network
    1.35 +
    1.36 +<LI><EM>n</EM>-process deadlock
    1.37 +
    1.38 +<LI>unordered channel
    1.39 +
    1.40 +<LI>reachability in directed graphs (section 6.4 of the book)
    1.41 +</UL>
    1.42 +
    1.43 +<P> Safety proofs (invariants) are often proved automatically.  Progress
    1.44 +proofs involving ENSURES can sometimes be proved automatically.  The
    1.45 +level of automation appears to be about the same as in HOL-UNITY by Flemming
    1.46 +Andersen et al.
    1.47 +
    1.48 +<HR>
    1.49 +<P>Last modified on $Date$
    1.50 +
    1.51 +<ADDRESS>
    1.52 +<A NAME="lcp@cl.cam.ac.uk" HREF="mailto:lcp@cl.cam.ac.uk">lcp@cl.cam.ac.uk</A>
    1.53 +</ADDRESS>
    1.54 +</BODY></HTML>