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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>