HOL theorem-proving system

Hi Ewa,

| This tip was terrific, I was able to define choice and also prove the 
| unconditional and weak fairness.

Great!

| I set the goal to be:
| [...]
| and I get error:  Types cannot be unified.

I think the problem is that "measure" expects a function mapping
into type ":num" (natural numbers), so the following subterm fails:

  measure (\(b,x). b = 1)

If I replace this with the following it typechecks (though I hasten
to add that it might not be correct for your theorem), since b is
already of type ":num" even though we think of it as Boolean:

  measure (\(b,x). b)

Unfortunately, HOL Light doesn't give very helpful error messages when
typechecking fails. One approach (how I found this problem) is to pick
a few small subterms and see if they typecheck in isolation, then
try larger ones to see when things start to interact badly. You can
also examine the type of free variables in a (sub)term like this:

  (map dest_var o frees) `..your term...`

which is sometimes helpful in tricky cases.

John.

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             SUBMISSION DEADLINE EXTENDED: APRIL 28

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     .----------------- Last Call for Papers -------------------

                         SMT Workshop '07
     5th International Workshop on Satisfiability Modulo Theories

         Previously called: Pragmatics of Decision Procedures
                   in Automated Reasoning (PDPAR)

      Berlin, Germany, 1-2 July 2007  (affiliated with CAV '2007)

                http://www.lsi.upc.edu/~oliveras/smt07

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Background
~~~~~~~~~~
Deciding the satisfiability of first-order formulas modulo background
theories, known as the Satisfiability Modulo Theories (SMT) problem,
has proved to be useful in verification, compiler optimization,
scheduling, and other areas.

The success of SMT techniques depends on the development of both
domain-specific decision procedures for each concrete theory
(e.g. linear arithmetic, the theory of arrays, or the theory of
bit-vectors) and combination methods that allow one to obtain more
versatile SMT tools. These two ingredients together make SMT
techniques well-suited for use in larger automated reasoning and
formal verification efforts.

Aims and Scope
~~~~~~~~~~~~~~
The aim of the workshop is to bring together researchers and users of
SMT tools and techniques. Continuing with the PDPAR tradition, we
especially encourage submission of papers focused on pragmatic
aspects. Relevant topics include but are not limited to:

* New decision procedures and new theories of interest
* Combination of decision procedures
* Novel implementation techniques
* Benchmarks and evaluation methodologies
* Applications and case studies
* Theoretical results

Important dates
~~~~~~~~~~~~~~~
Submission deadline                  : 28 April
Notification of acceptance/rejection : 21 May
Final version due                    : 4 June
Workshop                             : 1-2 July

Proceedings
~~~~~~~~~~~
Given the informal style of the workshop, only informal proceedings
will be distributed at the workshop. We are planning to publish a
selected subset of the submitted papers as post-proceedings in a
special volume of the Electronic Notes in Theoretical Computer Science
(ENTCS) unless the authors prefer not to.

Paper Submission and Proceedings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Following the PDPAR'06 initiative, there are two categories of
submissions:

* Original papers: contain original research (simultaneous submissions
  are not allowed) and sufficient detail to assess the merits and
  relevance of the submission. For papers reporting experimental
  results, authors are strongly encouraged to make their data
  available. Given the informal style of the workshop, we will  =20
  welcome work in progress and novel ideas that are not yet
  competitive in practice.

* Presentation-only papers: describe work recently published or
  submitted and will not be included in the proceedings. We see this
  as a way to provide additional access to important developments that
  SMT Workshop attendees may be unaware of.

Papers in both categories will be peer-reviewed. Papers should not =20
exceed 10 pages (Postscript or PDF) and should be written in LaTeX,
11pt, one column, a4paper, standard margins. Technical details may be
included in an appendix to be read at the reviewers' discretion. Full
submission guidelines are at the workshop web page.

Invited Speakers
~~~~~~~~~~~~~~~~

- Rupak Majumdar, University of California, Los Angeles.

- Peter O'Hearn, Queen Mary, University of London.


Student travel awards
~~~~~~~~~~~~~~~~~~~~~
SMT 2007 will partially reimburse some students for their
conference-related expenses. Preference will be given  =20
to students playing an active role in the workshop. However,
students in other situations are also encouraged to apply.

We require applications in the form of a short recommendation letter
written by the student's supervisor, to be sent to the PC chairs by
March 30.

Program Chairs
~~~~~~~~~~~~~~=20

- Sava Krstic, Intel Corporation
- Albert Oliveras, Tech. Univ. of Catalonia =20


Program Committee
~~~~~~~~~~~~~~~~~
Clark Barrett, New York University
Alessandro Cimatti, ITC-Irst, Trento
Byron Cook, Microsoft Research
Amit Goel, Intel Corporation
Aarti Gupta, NEC Labs America
Shuvendu Lahiri, Microsoft Research
Leonardo de Moura, Microsoft Research
Robert Nieuwenhuis, Technical University of Catalonia
Silvio Ranise, LORIA, Nancy
Roberto Sebastiani, Universita` di Trento
Ofer Strichman, Technion
Cesare Tinelli, University of Iowa
Ashish Tiwari, Stanford Research Institute (SRI)

SecReT 2007
    2nd International Workshop on Security and Rewriting Techniques
                  http://www.rdp07.org/secret.html

                           June 29, 2007
                           Paris, France

                   A satellite event of RDP 2007

======================================================================

SUBMISSION DEADLINE EXTENDED to Tuesday, May 1.

======================================================================



TOPICS OF INTEREST

The aim of this workshop is to bring together rewriting researchers and
security experts, in order to foster their interaction and develop future
collaborations in this area, to provide a forum for presenting new ideas
and work in progress, and to enable newcomers to learn about current
activities in this area.

The workshop focuses on the use of rewriting techniques in all aspects
of security. Specific topics include: authentication, encryption,
access control and authorization, protocol verification, specification
of policies, intrusion detection, integrity of information, control of
information leakage, control of distributed and mobile code, etc.


IMPORTANT DATES

     * Submissions:       Tuesday, May 1 (NEW)
     * Notification:      Monday, May 21
     * Final version due: Friday, June 8


SUBMISSION GUIDELINES

Authors are invited to submit a paper (max. 10 pages) in PDF or
PostScript format by April 23, 2007. Submissions should be sent by
email to Monica Nesi <monica at di dot univaq dot it>.

Preliminary proceedings will be available at the workshop. After the
workshop authors will be invited to submit a full paper of their
presentation. We plan to publish the accepted contributions in DMTCS.


INVITED SPEAKER

    * Thomas Genet  (Rennes, France)


PROGRAM COMMITTEE

    * Véronique Cortier  (Nancy, France)
    * Maribel Fernández (London, UK)
    * Paliath Narendran (Albany, NY, USA)
    * Monica Nesi (L'Aquila, Italy), co-chair
    * Tobias Nipkow (München, Germany)
    * Hitoshi Ohsaki (Osaka, Japan)
    * Graham Steel (Edinburgh, UK)
    * Mark-Oliver Stehr (Stanford, CA, USA)
    * Ralf Treinen (Cachan, France), co-chair
    * Luca Viganò (Verona, Italy)