**2IW55 (2014-2015) --- Algorithms for Model Checking**

*"Given a model of a system, exhaustively and automatically check whether this model meets a given specification. Typically, one has hardware or software systems in mind, whereas the specification contains safety requirements such as the absence of deadlocks and similar critical states that can cause the system to crash. Model checking is a technique for automatically verifying correctness properties of finite-state systems.*" (source: Wikipedia).

Model checking has applications in a diversity of areas such as software and hardware verification (as expected), but also in

*planning*,

*scheduling*,

*mechanical engineering, business process mining*and

*biology*. To understand the limitations of model checking, we study the mu-calculus, CTL* and some of its subsets such as LTL and CTL, from a computational viewpoint in these lectures. Among others, we treat the symbolic (fixed point based) algorithms for CTL, and fair CTL. The mu-calculus is discussed and its complexity is analysed. Transformations of the mu-calculus model checking problem to the frameworks of Boolean equation systems and Parity Games are addressed, combined with advanced algorithms for solving the latter artefacts.

**Objectives**

After
taking this course, students are expected
to

- be capable of explaining the computational complexity of the model checking algorithms for (fair) CTL and the modal mu-calculus
- be capable of transforming (fair) CTL formulae to the modal mu-calculus
- be able to explain the role of OBDDs in symbolic model checking
- be capable of simplifying Parity Games and parameterised Boolean equation systems
- be capable of explaining the computational complexity of the algorithms for solving Parity Games
- have the skills to manually execute the
algorithms for model checking (fair) CTL and the
modal mu-calculus
- be able to transform the problem of model checking to the modal mu-calculus to the problem of solving Boolean equation systems
- be able to transform the
problem of solving Boolean equation systems
to the problem of computing the winners in a Parity Game, and
*vice versa* - have the skills to manually solve (parameterised) Boolean equation systems and Parity Games using the algorithms presented in the course.

**Assessment**

The assessment consists of two assignments and a written examination. The weighting of the assignments and the examination are 30% and 70%, respectively. Students can successfully pass the course if a minimal score of 5.5 for the written examination is obtained and the average of both assignments is at least 5.5.

**Important Notes**

- Lectures are Tuesday afternoon (quarter 3) 13.45
-- 15.30 in
**Laplace 1.105**, and Wednesday morning (quarter 3) 08.45 -- 10.30 in MF 07 (I know... quite a challenge). -
Note: first lecture is
**Tuesday 3 February**. There are no lectures on 17, 18 February and 10,11 March. Last lecture is**Wednesday 25 March**. **Office hours**for discussing the course: on Monday from 11.15-12.00 and on Friday from 9.15-10.00. Drop me a mail if you wish to ensure I'm in my office.- The exam is on Wednesday 8 April,
13.30-16.30. There is a resit on Tuesday 23 June, 13.30-16.30 (but I
suggest you pass the first exam).
- The
exam is
**open book**, i.e., the book, handouts and slides may be used for consulting during the examination. Laptops, grannies and other auxiliaries are not allowed. - The 2012 lectures of this course have been recorded and can be viewed online (you do need to log in for this and be with an institute that struck the right kind of deal with the TU/e for this).
- Look for previous
incarnations of this course for some
**exams with solutions**(see teaching/past courses; the exams from 2010 can be found online, as well as a 2009 version)

**Course material**

- Additional reading (not mandatory, roughly covers the first 4 lectures): Model Checking. Edmund M. Clarke, Jr., Orna Grumberg, and Doron A. Peled. MIT Press, ISBN 0-262-03270-8.
- More
additional reading (not mandatory either, roughly covers the first 3
lectures, but offers a very nice read otherwise): Principles of Model
Checking. Christel Baier and Joost-Pieter Katoen. MIT Press, ISBN
978-0-262-02649-9.
- Handouts, which will be made available for download below (updated regularly).
- 11 Feb: E.A. Emerson and C.-L. Lei: Model Checking in the Propositional Mu-Calculus
- 24 Feb: A. Mader: Verification of Modal Properties Using Boolean Equation Systems
- 25 Feb: J.J.A. Keiren: An experimental study of algorithms and optimisations for parity games, with an application to Boolean Equation Systems
- 03 Mar: M. Gazda and T.A.C. Willemse: Zielonka's Recursive Algorithm: dull, weak and solitaire games and tighter bounds
- 03 Mar: O. Friedmann: Recursive solving of parity games requires exponential time
- 04 Mar: M. Jurdzinski: Small Progress Measures for Solving Parity Games
- 04 Mar: H. Klauck: Algorithms for Parity Games
- 17 Mar: B. Ploeger, J.W. Wesselink, T.A.C. Willemse: Verification of Reactive Systems via Instantiation of Parameterised Boolean Equation Systems
- 17 Mar: J.F. Groote, T.A.C. Willemse: Parameterised Boolean Equation Systems
- 18 Mar: S. Cranen, B. Luttik and T.A.C. Willemse, Proof Graphs for Parameterised Boolean Equation Systems
- 18 Mar: J.F. Groote and T.A.C. Willemse: Model-checking processes with data (note: there is a subtle mistake in the Par function in that paper; take the definition from the slides).
- 24 Mar: S. Orzan and T.A.C. Willemse: Static Analysis
Techniques for Parameterised Boolean Equation
Systems
- Assignments.
Yes, these too, two of'em, were made available for download below.
Assignments were briefly introduced/explained during the lectures.
**Caution: the assignments involve some programming and take time. Plan carefully. Assignments can be made in small groups (3 students).** **Research.**If (you think) you enjoy doing research (individually or in a small group) in the intersection of algorithms, logics, game theory or their application, feel free to contact me (or approach me during the lectures): I have some topics that might interest you. Of course, you can also propose your own topics.

**Topics and Course notes**

*Part I: 03 Feb - 11 Feb. Exercises can be downloaded from here*

- 03
Feb: Domestic Announcements (slides) and the
temporal logics CTL*, CTL and LTL (slides)
- 04
Feb: Symbolic model checking for CTL (slides)
- 10
Feb: Symbolic model checking: Fairness and Counterexamples (slides)
- 11
Feb: The mu-calculus (slides)

*Part II: 24 Feb - 04 Mar. Exercises for Part II and III can be downloaded from here*

- 24
Feb: Boolean Equation Systems (slides)
- 25
Feb: Parity Games (slides)
- 03
Mar: Recursively Solving Parity Games (slides)
- 04
Mar: Small Progress Measures (slides)

*Part III: 17 Mar - 25 Mar.*

- 17 Mar: Parameterised
Boolean Equation Systems 1 (slides)
- 18
Mar: Parameterised Boolean Equation Systems 2 (slides)
- 24
Mar: Parameterised Boolean Equation Systems 3 (slides)
- 25
Mar: Wrap-up (slides, exercise, solution)