Proof Obligations of the B Formal Method: Local Proofs Ensure Global Consistency

The B formal method has been successfully used in large projects and is not reserved to experts. The main correctness criterion of B is that every piece of code must preserve invariant properties. In this article, we briefly introduce the basic notions of B. We then concentrate on the proof obligations. After introducing them, we show how the sum of local proofs makes a global consistency. We believe that this strong modularity is essential for the tractability of the proofs.