# FAQ

## Contents

- 1 General
- 2 General Tool Usage?
- 3 Modeling
- 3.1 Witness for Xyz missing. Default witness generated
- 3.2 Identifier Xyz should not occur free in a witness
- 3.3 In INITIALISATION, I get
*Witness Xyz must be a disappearing abstract variable or parameter* - 3.4 I've added a witness for Xyz but it keeps saying
*"Identifier Xyz has not been defined"* - 3.5 What are type expressions in Event-B?

- 4 Proving
- 5 How to contribute and develop ?

## General

### What is event-B?

**Event-B** is a formal method for system-level modelling and analysis. Key features of event-B are the use of set theory as a modelling notation, the use of refinement to represent systems at different abstraction levels and the use of mathematical proof to verify consistency between refinement levels. More details are available in http://www.event-b.org/

### What is the difference between event-B and the B method?

Event-B is derived from the B method. Both notations have the same inventor, and share many common concepts (set-theory, refinement, proof obligations, ...) However, they are used for quite different purpose. The B method is devoted to the development of *correct by construction* software, while the purpose of event-B is to model full systems (including hardware, software and environment of operation).

Both notations use a mathematical language which are quite close but do not match exactly (in particular, operator precedences are different).

### What is Rodin?

The **Rodin Platform** is an Eclipse-based IDE for Event-B that provides effective support for refinement and mathematical proof. The platform is open source, contributes to the Eclipse framework and is further extendable with plugins.

### Where does the *Rodin* name come from?

The Rodin platform was initially developed within the European Commission funded Rodin project (IST-511599 ), where Rodin is an acronym for "Rigorous Open Development Environment for Complex Systems” . Rodin is also the name of a famous French sculptor, one of his most famous work being the Thinker.

## General Tool Usage?

### How do I install external plug-ins without using Eclipse Update Manager?

Although it is preferred to install additional plug-ins into the Rodin platform using the Update Manager of Eclipse, this might not always be practical. In this case, a manner to install these plug-ins is to emulate either manually or using ad-hoc scripts the operations normally performed by the Update Manager.

This manual installation of plug-ins is described in *Installing external plug-ins manually*.

### The builder takes too long

Generally, the builder spends most of its time attempting to prove POs. There are basically two ways to get it out of the way:

- the first one is to disable the automated prover in the Preferences panel.
- the second one is to mark some PO as reviewed when you don't want the auto-prover to attempt them anymore.

Note that if you disable the automated prover, you always can run it later on some files by using the contextual menu in the event-B Explorer.

To disable the automated prover, open Rodin `Preferences` (menu ). In the tree in the left-hand panel, select . Then, in the right-hand panel ensure that the checkbox labelled `Enable auto-tactic for proving` is disabled.

To review a proof obligation, just open it in the interactive prover, then click on the *review* button (this is a round blue button with a *R* in the proof control toolbar). The proof obligation should now labelled with the same icon in the event-B explorer.

### What are the ASCII shortcuts for mathematical operators

The ASCII shortcuts that can be used for entering mathematical operators are described in the help of the event-B keyboard plug-in. In the help system, this page has the following path

.This page is also available in the dynamic help system. The advantage of using dynamic help is that it allows to display the help page side-by-side with the other views and editors. To start the dynamic help, click

, then click and select the page in the tree.

### Rodin (and eclipse) doesn't take into account the MOZILLA_FIVE_HOME environment variable

You have to add a properties by appending the following code to your`eclipse/eclipse.ini`

`rodin/rodin.ini`

-Dorg.eclipse.swt.browser.XULRunnerPath=/usr/lib/xulrunner/xulrunner-xxx

## Modeling

### Witness for Xyz missing. Default witness generated

A parameter as disappeared during a refinement. If this is intentional, you have to add a witness telling how the abstract parameter is refined.

### Identifier Xyz should not occur free in a witness

You refer to ### In INITIALISATION, I get *Witness Xyz must be a disappearing abstract variable or parameter*

The witness is for the after value of the abstract variable, hence you should use the primed variable. The witness label should be ### I've added a witness for Xyz but it keeps saying *"Identifier Xyz has not been defined"*

As specified in the modelling language manual, the witness must be labelled by the name ### What are type expressions in Event-B?

The type expressions are defined recursively as follows:

- Built-in types: ℤ, BOOL (Note that ℕ is NOT a type expressions).

- Any carrier set is a type expression.

- If <math>T</math> is a type expression then <math>ℙ(T)</math> is a type expression.

- If <math>S</math> and <math>T</math> are type expressions then <math>S × T</math> is a type expression.

## Proving

### How can I do a Proof by Induction?

This page about proof by induction will give you some starting tips.

### Labels of proof tree nodes explained

- ahmeans
*add hypothesis*, - ehmeans rewrite with
*equality from hypothesis*from left to right, - hemeans rewrite with
*equality from hypothesis*from right to left, - rvtell us that this goal as been manually reviewed,
- sl/dsmeans
*selection/deselection*, - PPmeans
*discharged by the predicate prover* - MLmeans
*discharged by the mono lemma prover*

## How to contribute and develop ?

See the Developer FAQ page.