ing WS1S Systems to Verify Parameterized Networks . . . . . . . . . . . . 188 Kai Baukus, Saddek Bensalem, Yassine Lakhnech and Karsten Stahl FMona: A Tool for Expressing Validation Techniques over Infinite State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 J.-P. Bodeveix and M. Filali Transitive Closures of Regular Relations for Verifying Infinite-State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 Bengt Jonsson and Marcus Nilsson Diagnostic and Test Generation Using Static Analysis to Improve Automatic Test Generation . . . . . . . . . . . . . 235 Marius Bozga, Jean-Claude Fernandez and Lucian Ghirvu Efficient Diagnostic Generation for Boolean Equation Systems . . . . . . . . . . . . 251 Radu Mateescu Efficient Model-Checking Compositional State Space Generation with Partial Order Reductions for Asynchronous Communicating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Jean-Pierre Krimm and Laurent Mounier Checking for CFFD-Preorder with Tester Processes . . . . . . . . . . . . . . . . . . . . . . . 283 Juhana Helovuo and Antti Valmari Fair Bisimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Thomas A. Henzinger and Sriram K. Rajamani Integrating Low Level Symmetries into Reachability Analysis . . . . . . . . . . . . . 315 Karsten Schmidt Model-Checking Tools Model Checking Support for the ASM High-Level Language . . . . . . . . . . . . . . 331 Giuseppe Del Castillo and Kirsten Winter Table of

Tools and Algorithms for the Construction and Analysis of Systems. Proc. TACAS 2009

Twenty-five years ago, as an American GP living and practising in Wales, I would watch BBC sports programmes, such as darts and bowls and snooker, all unknown to me and, therefore, fascinating. I always found it odd — pairings such as Scotland (or Wales) versus The Rest of the World. It either seemed overly ambitious for Scotland or slim pickings for the rest of the world. After the recent US presidential election, it appears as if it will continue to be the US versus The Rest of the World.

Three books might help you, who are of ‘the rest of the world’, begin to grapple with what is going on in the US. Written from the short, medium, and long view, each has a somewhat parochial twist. Each also, however, contains a great deal of useful history.

The 9/11 Commission Report refutes the old saw that nothing good can be written by a committee. The report is a remarkable book and its recent nomination as a finalist for the National Book Award is a first for a government document, and well deserved. What is contained in this report is well known by most of us — the cast of characters has been in the news for over 3 years. And the sequence of events and many of the details that were gleaned from the ongoing hearings have been contained in news stories, long and short. However, to have published what is known until this point in a single narrative, which is at once accessible and clearly written, is a truly historical achievement. Reading the events of the day — regarding the planes that crashed in the city of New York, as the rescue squads from police and fire departments move into place and act — is both familiar and detailed in a way that helps us understand better than I would ever have imagined the why and how of all the death and destruction.

So much about those days have been parsed into documentaries — long analyses of causation of issues, like why the towers fell — that one would think that everything that could be written had been. But the Commission's report really does add enormous amounts of history to the sound bites and 30-second visuals that have pervaded politics and the world assessment of the US since that time. The report deals extensively and thoughtfully with the history of Islam, both ancient and recent, and describes the history of terrorism as it evolved from highjackings of the 1970s to the use of bombs and targeted destruction of military targets in the late 1980s and 1990s.

Events that occurred in the time that preceded the attacks of 9/11 are written in a way that shows the convergence of intelligence reports, a long history of threats from Bin Laden, and many alerts and warnings (‘the system was blinking red’ in the words of Tenet, CIA director). The information about the movements of the terrorists in their planning and the worldwide involvement of cells, support systems, and finances makes it clear that these events were truly the result of a network that reaches virtually everywhere.

After the attacks, reading of the efforts of the fire, police, and other rescue squads in New York adds specifics that are terrible and remarkable. On 9/11, I ran up and down the stairs between patients to watch on television as it was all happening. All of us who watched that day wondered what those people who were clearly doomed were thinking, feeling, and seeing. Their actual words in this report are not fiction, they are the words, for most the last words, of people who died as we watched. Their words are the hardest part of this long, detailed report to deal with.

Much of the final third of the report is devoted to what a fire captain friend of mine once called a PFE — a post-fire evaluation — which he mandated for his squad after every fire. In a PFE, the entire squad reconstructed, relived, and discussed the events to see what could be improved next time. The 9/11 Commission engaged in a world-scale PFE. Although all US politicians state that they intend to follow the recommendations of The 9/11 Commission Report, the backing and filling is already well underway. What politician, for example, is going to agree that major conurbations, and political and tactical targets should receive preference over their hometown fire departments and that homeland security money should ‘not be used as a pork barrel’?

Rather than bringing a grieving country together in a way that will make such events unlikely to happen again, the reactions from the report have begun to cleave along party lines once again. The 9/11 Commission was almost unique in its thoroughness, transparency, and its ability to focus on the real issue of terror and lawlessness. However, the extent to which a violent stateless ideology has negatively affected the tolerance of differences, the sense of community, and the level of civic discourse in the US means that terrorism has affected our neighborhoods as much as it has affected our country. And fear rather than determination, despite the President's stump speech, has become the dominant emotion.

Robert Byrd, from his 45-year perspective in the US Senate, understands that cheques and balances are essential to avoid tragedy, even if they, at times, impede progress. His book, Losing America, contains several ‘under-the-table’ looks at Congress and the manipulations and arrogance of the coterie of ideologues who surround George W. Bush. Byrd, from the Southern tradition of politeness and respect, which often cloaks bar-room politics, is steeped in the history of the institution of the Senate. He is personally offended by Bush's lack of interest or curiosity in the legislative process prior to 9/11, and his dishonesty and deception afterwards. Byrd's address to the Senate on the eve of the war on Iraq was widely quoted and is contained in this book. While people marching in the streets made headlines, it was an 85-year-old senator, not previously known as an outraged progressive, who took on both the Administration for its hypocrisy and many of his colleagues for their lack of courage and principle. He voted against the war and continues to point out the dishonesty of the people who guide it. The book reads with a sensibility from another age. Although his own history is certainly not without problems, Senator Byrd's belief in the true democratic process, rather than the gun-barrel approach of George W. Bush, should be given the respect that he, and it, deserve.

Arthur Schlesinger Jr has been writing history since 1946 and has Pulitzer prizes to prove he does it well. His voice is considered, thoughtful, and scholarly — as one might expect from a historian and distinguished teacher. Toward the end of his book War and the American Presidency, however, Schlesinger's voice rises with outrage at those who surround and influence George W. Bush, the ‘small group of Messianic statesman whose self righteousness bids fair to wreck our age’. He writes of the imperial presidencies of the early years of the country, which repressed dissent during wartime, and how the US moved from wars based on pique to engaging international diplomacy and internationalism. Schlesinger reminds us that all presidents since Wilson, with George W. Bush being the glaring exception, believed in statesmanship, diplomacy, alliances to guard against capricious choices and, when necessary, taking on common enemies.

Much of Schlesinger's book, however, also chronicles the record of the current Administration which, by being ‘judge, jury, and executioner resurrects the imperial presidency’. An imperial presidency in the age of frigates and single-shot rifles cannot be compared with one that possesses weapons of mass destruction and a wooly-headed sense of divine guidance. We used to think of Henry Kissinger as the prototype for Dr Strangelove, but I wish Kubrick were still alive to do the remake with Dick Cheney and Donald Rumsfeld in mind.

Needless to say, the recent election, instead of relegating George W. Bush and his hangers-on to the historical trashbin, has pushed them to the front of the international agenda. A secretive, defensive, unreflective president will now shape the world for our grandchildren. Each of these books elaborates on the ineffectiveness of Bush dealing with the real enemy while he digs deeper into a country where he is creating more enemies by the day.

One has to ask why, instead of quietly writing their memoirs, two distinguished 87-year-old statesmen are raising the alarm and shaking us by the throat — like the aging Thomas Jefferson who, in his famous letter of 1820, said of the first compromise to try to divide the country between slave and free states: ‘this momentous question, like a firebell in the night, awakened and filled me with terror’. Byrd and Schlesinger hear the firebell and are ringing it to wake us up. Another quote that might better capture Bush and his legacy would be from the Bible he uses as justification for his policies: ‘He that troubleth his own house shall inherit the wind’ (Proverbs 11, 29).

The 9/11 Commission Report: Final Report of the National Commission on Terrorist attacks upon the United States.

Handbook of logic in computer science.

This paper describes a compositional shape analysis, where each procedure is analyzed independently of its callers. The analysis uses an abstract domain based on a restricted fragment of separation logic, and assigns a collection of Hoare triples to each procedure; the triples provide an over-approximation of data structure usage. Compositionality brings its usual benefits -- increased potential to scale, ability to deal with unknown calling contexts, graceful way to deal with imprecision -- to shape analysis, for the first time.The analysis rests on a generalized form of abduction (inference of explanatory hypotheses) which we call bi-abduction. Bi-abduction displays abduction as a kind of inverse to the frame problem: it jointly infers anti-frames (missing portions of state) and frames (portions of state not touched by an operation), and is the basis of a new interprocedural analysis algorithm. We have implemented our analysis algorithm and we report case studies on smaller programs to evaluate the quality of discovered specifications, and larger programs (e.g., an entire Linux distribution) to test scalability and graceful imprecision.

/pdf/compositional-shape-analysis-by-means-of-bi-abduction-3k7rt4zvp8.pdf

Compositional shape analysis by means of bi-abduction

Many network applications, eg, industrial control, demand ultra-low latency (ULL) However, traditional packet networks can only reduce the end-to-end latencies to the order of tens of milliseconds The IEEE 8021 time sensitive networking (TSN) standard and related research studies have sought to provide link layer support for ULL networking, while the emerging IETF deterministic networking (DetNet) standards seek to provide the complementary network layer ULL support This paper provides an up-to-date comprehensive survey of the IEEE TSN and IETF DetNet standards and the related research studies The survey of these standards and research studies is organized according to the main categories of flow concept, flow synchronization, flow management, flow control, and flow integrity ULL networking mechanisms play a critical role in the emerging fifth generation (5G) network access chain from wireless devices via access, backhaul, and core networks We survey the studies that specifically target the support of ULL in 5G networks, with the main categories of fronthaul, backhaul, and network management Throughout, we identify the pitfalls and limitations of the existing standards and research studies This survey can thus serve as a basis for the development of standards enhancements and future ULL research studies that address the identified pitfalls and limitations

Ultra-Low Latency (ULL) Networks: The IEEE TSN and IETF DetNet Standards and Related 5G ULL Research

We give a simple and efficient method to prove safety properties for parameterized systems with linear topologies. A process in the system is a finite-state automaton, where the transitions are guarded by both local and global conditions. Processes may communicate via broadcast, rendez-vous and shared variables. The method derives an over-approximation of the induced transition system, which allows the use of a simple class of regular expressions as a symbolic representation. Compared to traditional regular model checking methods, the analysis does not require the manipulation of transducers, and hence its simplicity and efficiency. We have implemented a prototype which works well on several mutual exclusion algorithms and cache coherence protocols.

https://link.springer.com/content/pdf/10.1007%2F978-3-540-71209-1_56.pdf

Regular model checking without transducers (on efficient verification of parameterized systems)

We present a decision procedure for a logic that combines (i)aword equations over string variables denoting words of arbitrary lengths, together with (ii)aconstraints on the length of words, and on (iii)athe regular languages to which words belong. Decidability of this general logic is still open. Our procedure is sound for the general logic, and a decision procedure for a particularly rich fragment that restricts the form in which word equations are written. In contrast to many existing procedures, our method does not make assumptions about the maximum length of words. We have developed a prototypical implementation of our decision procedure, and integrated it into a CEGAR-based model checker for the analysis of programs encoded as Horn clauses. Our tool is able to automatically establish the correctness of several programs that are beyond the reach of existing methods.

/pdf/string-constraints-for-verification-28j03xy2oe.pdf

String Constraints for Verification

We present a simple and effective approximated backward reachability algorithm for parameterized systems with existentially and universally quantified global conditions. The individual processes operate on unbounded local variables ranging over the natural numbers. In addition, processes may communicate via broadcast, rendez-vous and shared variables. We apply the algorithm to verify mutual exclusion for complex protocols such as Lamport's bakery algorithm both with and without atomicity conditions, a distributed version of the bakery algorithm, and Ricart-Agrawala's distributed mutual exclusion algorithm.

/pdf/parameterized-verification-of-infinite-state-processes-with-1z3ayt28sp.pdf

Parameterized verification of infinite-state processes with global conditions

We present version 1.0 of the Norn SMT solver for string constraints. Norn is a solver for an expressive constraint language, including word equations, length constraints, and regular membership queries. As a feature distinguishing Norn from other SMT solvers, Norn is a decision procedure under the assumption of a set of acyclicity conditions on word equations, without any restrictions on the use of regular membership.
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/pdf/norn-an-smt-solver-for-string-constraints-13540b8j24.pdf

Norn: An SMT Solver for String Constraints

We give a sound and complete fence insertion procedure for concurrent finite-state programs running under the classical TSO memory model. This model allows "write to read" relaxation corresponding to the addition of an unbounded store buffer between each processor and the main memory. We introduce a novel machine model, called the Single-Buffer (SB) semantics, and show that the reachability problem for a program under TSO can be reduced to the reachability problem under SB. We present a simple and effective backward reachability analysis algorithm for the latter, and propose a counter-example guided fence insertion procedure. The procedure is augmented by a placement constraint that allows the user to choose places inside the program where fences may be inserted. For a given placement constraint, we automatically infer all minimal sets of fences that ensure correctness. We have implemented a prototype and run it successfully on all standard benchmarks together with several challenging examples that are beyond the applicability of existing methods.

/pdf/counter-example-guided-fence-insertion-under-tso-2sae6zga55.pdf

Ahmed Rezine

Papers

Regular model checking without transducers (on efficient verification of parameterized systems)

String Constraints for Verification

Parameterized verification of infinite-state processes with global conditions

Norn: An SMT Solver for String Constraints

Counter-Example guided fence insertion under TSO