The most expensive source of errors and the more difficult to detect in a formal development is the error during specification. Hence, the first step in a formal development usually consists in exhibiting the set of all behaviors of the specification, for instance with an automaton. Starting from this observation, many researches are about the generation of a B machine from a behavioral specification, such as UML. However, no backward verification are done. This is why, we propose the GeneSyst tool, which aims at generating an automaton describing at least all behaviors of the specification. The refinement step is considered and appears as sub-automatons in the produced SLTS.