# Extending the Proof Manager

The Proof Manager is responsible for constructing proofs and maintaining existing proofs associated with proof obligations.

There are two ways for extending the Proof Manager:

- adding a new reasoner.

- adding a new tactic.

## Adding a New Reasoner

A reasoner is added into the Proof Manager using the extension point *org.eventb.core.seqprover.reasoners*. Below is an example of how to contribute to the extension point.

<extension point="org.eventb.core.seqprover.reasoners"> <reasoner class="org.eventb.contributors.seqprover.reasoners.Hyp" id="hyp" name="%hypName"/> </extension>

where the *name* attribute is internationalized.

The above declaration defines a reasoner with a specific *id* (which will be automatically prefixed by the project name, e.g. *org.eventb.contributors.seqprover*).

The *class* attribute must be a valid *Java* class name which will be used to create an instance of the reasoner. This class must implements *org.eventb.core.seqprover.IReasoner* interface.

However, most of the time, the developers only need to sub-class one of the abstract implementation, depending on the type of the reasoner. For the implementation purpose, we categorize our reasoners into the following types.

- Automatic rewrite Reasoners of this type apply some rewriting rules automatically to simplify the input sequent.

- Manual rewrite Reasoners of this type apply a rewriting rule for a given formula (or sub-formula) in the goal or in one of the hypotheses.

- Automatic inference Reasoners of this type apply an inference rule automatically.

- Manual inference Reasoner of this type apply an inference rule manually.

- General purpose Reasoners that do not fall into the four previous categories.

*Please also have a look at* How To Evolve Reasoners.

## Adding a New Tactic

Adding a reasoner is only a first step in extending the Proof Manager. Reasoners need to be wrapped by Tactics for the Proof Manager to use. Similar to reasoners, there are different types of tactics for implementation purpose.

### Implementing a Tactic

- Automatic Tactics: Tactics that can be run automatically either as POM Tactics or Post Tactics.

- Manual Tactics : Tactics that need to be invoke manually during interactive proofs.