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+<H2>UNITY--Chandy and Misra's UNITY formalism</H2>
+
+<P>The book <EM>Parallel Program Design: A Foundation</EM> by Chandy and Misra
+(Addison-Wesley, 1988) presents UNITY, which consists of an abstract
+programming language of guarded assignments and an associated calculus.
+Misra's 1994 paper "A Logic for Concurrent Programming" presents "New UNITY",
+giving more elegant foundations for a more general class of languages.
+
+<P> This directory is a preliminary formalization of New UNITY.  The Isabelle
+examples may not represent the most natural treatment of UNITY style.  Hand
+UNITY proofs tend to be written in the forwards direction, as in informal
+mathematics, while Isabelle works best in a backwards (goal-directed) style.
+
+<P>
+The syntax, also, is rather unnatural.   Programs are expressed as sets of 
+commands, where each command is a relation on states.  Quantification over 
+commands using [] is easily expressed.  At present, there are no examples of
+quantification using ||.
+
+<P>
+The directory presents a few small examples, mostly taken from Misra's 1994
+paper:
+<UL>
+<LI>common meeting time
+
+<LI>the token ring
+
+<LI>the communication network
+
+<LI><EM>n</EM>-process deadlock
+
+<LI>unordered channel
+
+<LI>reachability in directed graphs (section 6.4 of the book)
+</UL>
+
+<P> Safety proofs (invariants) are often proved automatically.  Progress
+proofs involving ENSURES can sometimes be proved automatically.  The
+level of automation appears to be about the same as in HOL-UNITY by Flemming
+Andersen et al.
+
+<HR>
+<P>Last modified on $Date$
+
+<ADDRESS>
+<A NAME="lcp@cl.cam.ac.uk" HREF="mailto:lcp@cl.cam.ac.uk">lcp@cl.cam.ac.uk</A>
+</ADDRESS>
+</BODY></HTML>