Animating and Model Checking B Specifications with Higher-Order Recursive Functions

The B-method [1] is a theory and methodology for formal development of computer systems. It is used in industry in a range of critical domains. In addition to the proof activities it is increasingly being realised that validation of the initial specification is important, as otherwise a correct implementation of an incorrect specification is being developed. This validation can come in the form of animation, e.g., to check that certain functionality is present in the specification. Another useful tool is model checking, whereby the specification can be systematically checked for certain temporal properties. In previous work [2], we have presented the ProB animator and model checker to support those activities. In this work we present two important improvements upon previous work. First, realistic specifications often contain complicated functions. Take the following excerpt of a specification (translated from a Z specification given to us by Anthony Hall):