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The ProB Disprover plugin for RODIN utilizes the ProB animator and model checker to automatically find counterexamples
The ProB Disprover plugin for RODIN utilizes the ProB animator and model checker to automatically find counterexamples
for a given problematic proof obligation.
or proofs for a given proof obligation.


The Disprover is described in [http://www.stups.uni-duesseldorf.de/publications_detail.php?id=219 Debugging Event-B Models using the ProB Disprover Plug-in], Ligot, Bendisposto, Leuschel.
The Disprover is described in [http://www.stups.uni-duesseldorf.de/publications_detail.php?id=219 Debugging Event-B Models using the ProB Disprover Plug-in], Ligot, Bendisposto, Leuschel.
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== Installation ==
== Installation ==


The ProB Disprover is available through the ProB Update Site.  To Install it:
The ProB Disprover is currently only available through the ProB Nightly Build Update Site (http://nightly.cobra.cs.uni-duesseldorf.de/rodin/updatesite/).   


* Go to the Update manager (Help -> Software Updates...)
* Open the ProB Update Site (http://www.stups.uni-duesseldorf.de/update)
* Select all items under "ProB Disprover"


== How to use it, how it works ==
== How to use it, how it works ==


The proof obligation editor in Rodin presents the user with a number of Hypotheses and one Goal, to be proved.  If the Disprover is installed, it is available in the tool bar alongside the other provers.
[[Image:disprover-all.png]]: The proof obligation editor in Rodin presents the user with a number of Hypotheses and one Goal, to be proved.  If the Disprover is installed, it is available in the tool bar alongside the other provers.


Upon selecting the Disprover, it builds an Event-B context from the Hypotheses and the Goal (see below).  The ProB model checker then tries to set up the constants.  If that is possible, this state is a counter example that will be presented back to the user in the proof tree.
Upon selecting the Disprover, it builds a formula from the Hypotheses and the negated Goal.  The ProB model checker then tries to find a model for that formula.  If that is possible, this model is a counter example that will be presented back to the user in the proof tree. The disprover also checks if there cannot be a model for the formula. If this is the case it acts like a decision procedure, i.e., absence of a model is a proof for the goal. Unfortunately, sometimes neither a counter example nor a proof can be found.  


Unfortunately, if no counter example is found, there may still be a solution, so we cannot consider the proof to be discharged.  Thus, the Disprover will merely mark the proof as "Reviewed".
There are a number of different modes for the Disprover, all with advantages and disadvantages.
== The Disprover-Modes ==
[[Image:disprover-relevant-context.png]] '''Using relevant Hypotheses and includes all Contexts''': Rodin determines which Hypotheses it considers relevant, uses those and includes all Context Information (Sets, Constants, Axioms).
[[Image:disprover-all.png]] '''Uses all Hypotheses''':  Simply all Hypotheses are used.  As this includes the Axioms from the Contexts as well, including them would be redundant.
[[Image:disprover-config.png]] '''Allows detailed configuration of the Disprover parameters''': A dialog allows the Disprover to be configured in great detail. Warning: If inproperly used, this may result in counter-examples that are not really counter-examples.
[[Image:disprover-relevant.png]] '''Includes only the relevant hypotheses''':  Only those hypotheses that Rodin considers relevant are included.  This may result in counter-examples that are not really counter-examples, so this mode is discouraged.
== Disprover-Preferences ==
There is an entry for the Disprover in the preferences.  These are the same preferences that are presented to the user when running in the configuration mode.  These preferences are NOT used for the other modes.  When using another use, the ProB-Preferences are used.
== The newly constructed context and machine ==
The generated machine is completely empty (besides an empty INITIALISATION event).  It is only generated, because ProB requires it.
The context contains:
* The negated Goals as an Axiom
* The Hypotheses, as Axioms
* The Variables, as Constants
* The Sets
* The Constants
In some modes, those Contexts that are referred from the Sequent are referred through SEES clauses.


[[Category:User documentation]]
[[Category:User documentation]]

Revision as of 13:36, 9 April 2013

ProB Disprover

The ProB Disprover plugin for RODIN utilizes the ProB animator and model checker to automatically find counterexamples or proofs for a given proof obligation.

The Disprover is described in Debugging Event-B Models using the ProB Disprover Plug-in, Ligot, Bendisposto, Leuschel.

Installation

The ProB Disprover is currently only available through the ProB Nightly Build Update Site (http://nightly.cobra.cs.uni-duesseldorf.de/rodin/updatesite/).


How to use it, how it works

: The proof obligation editor in Rodin presents the user with a number of Hypotheses and one Goal, to be proved. If the Disprover is installed, it is available in the tool bar alongside the other provers.

Upon selecting the Disprover, it builds a formula from the Hypotheses and the negated Goal. The ProB model checker then tries to find a model for that formula. If that is possible, this model is a counter example that will be presented back to the user in the proof tree. The disprover also checks if there cannot be a model for the formula. If this is the case it acts like a decision procedure, i.e., absence of a model is a proof for the goal. Unfortunately, sometimes neither a counter example nor a proof can be found.

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