Rewriting rules for event model decomposition
From Event-B
The purpose of this page is to list and justify the rewriting / simplification rules applied in the event model decomposition when building the external events, and more especially their actions.
Rewriting rules for the Event-B assignments
As detailed in the modelling language, the Event-B assignments are formed of two parts:
- a left-hand side, which is a list of free identifiers.
- a right-hand side.
There are various kinds of assignments:
- The ("becomes such that") assignment is the most general (non-deterministic) assignment, where a predicate is given on the before and after values of assigned identifiers. The after values of the assigned identifiers are denoted by a primed identifier whose prefix is the assigned identifier.
- The ("becomes equal to") assignment is the deterministic assignment where an expression is given for each assigned identifier.
- The ("becomes member of") assignment is the set-based (non-deterministic) assignment, where a set expression is given for the assigned identifier.
Let and be variables, and and be expressions. In the following table, the left-hand assignments are equivalent () to the right-hand ones:
Thus, each Event-B assignment can be expressed in a "becomes such that" form.
Simplification rules on Event-B predicates
Rewriting rules for the Event-B actions
Let and be variables, and and be predicates. The following equivalence applies :