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14 <H2>UNITY--Chandy and Misra's UNITY formalism</H2>
16 <P>The book <EM>Parallel Program Design: A Foundation</EM> by Chandy and Misra
17 (Addison-Wesley, 1988) presents the UNITY formalism. UNITY consists of an
18 abstract programming language of guarded assignments and a calculus for
19 reasoning about such programs. Misra's 1994 paper "A Logic for Concurrent
20 Programming" presents New UNITY, giving more elegant foundations for a more
21 general class of languages. In recent work, Chandy and Sanders have proposed
22 new methods for reasoning about systems composed of many components.
24 <P>This directory formalizes these new ideas for UNITY. The Isabelle examples
25 may seem strange to UNITY traditionalists. Hand UNITY proofs tend to be
26 written in the forwards direction, as in informal mathematics, while Isabelle
27 works best in a backwards (goal-directed) style. Programs are expressed as
28 sets of commands, where each command is a relation on states. Quantification
29 over commands using [] is easily expressed. At present, there are no examples
30 of quantification using ||.
32 <P>A UNITY assertion denotes the set of programs satisfying it, as
33 in the propositions-as-types paradigm. The resulting style is readable if
36 <P> Safety proofs (invariants) are often proved automatically. Progress
37 proofs involving ENSURES can sometimes be proved automatically. The
38 level of automation appears to be about the same as in HOL-UNITY by Flemming
42 The directory <A HREF="Simple/"><CODE>Simple</CODE></A>
43 presents a few examples, mostly taken from Misra's 1994
44 paper, involving single programs.
45 The directory <A HREF="Comp/"><CODE>Comp</CODE></A>
46 presents examples of proofs involving program composition.
49 <P>Last modified on $Date$
52 <A NAME="lcp@cl.cam.ac.uk" HREF="mailto:lcp@cl.cam.ac.uk">lcp@cl.cam.ac.uk</A>